Turn off water to front bathroom

The question is not stupid, but I don't think it's easy to answer it, also for anyone who knows the boat model.
Wouldn't it be simpler to ask the chap you had onboard what did he do?

Actually, I'd guess that he opened a valve rather than turn a switch on, because any electrical switch is likely to control the pump, and I don't think you have more than one, considering the boat size.
So, if previously you had water elsewhere and no leak from the front bathroom, more than likely you had a valve closed along the pipe feeding the bathroom, and the leak started after that guy opened it.

Usually water pipes run along the hull sides. Start looking on the side the head is located. Also, find the water pump and trace from there

I hate to say this but if you don’t know the difference between a valve to shut down fresh water and a seawater thru hull... you need to hire someone to teach you about boat systems.

a fresh water leak from your forward head is no big deal but if a raw water hose pops a leak you need to know how to how to stop it

I don't think either.
The strainer is the canister shape thing that you found along the hull intake pipe, and is meant to filter garbage that might be sucked together with the sea water. You don't have anything like that in the fresh water circuit.
Did he possibly mention an electrical pump, or an accumulator tank, or a heater?
Those are the bits of kit normally installed in the fresh water circuit.

Regardless, for opening/closing hydraulic lines, there must be valves, possibly attached to any of these components.
So, in principle you should look for a valve similar to the one which you found attached to the thru-hull intake - just smaller, more than likely.
They are called "ball valves", and they come in several different materials (hence colors) and sizes.
Besides, they can either be made with a lever or a T-handle, mostly depending on the valve size.
If you take some pics of the e/r and post them, it might be easier to give you some more specific suggestion.

But beware of one thing, in the meantime:
when Pascal said that a fresh water leak is no big deal, he was assuming that you are using the onboard fresh water tank.
If so, in the worst case the leak could fill the boat bottom with as much fresh water as there is in the tank - very annoying, but not catastrophic.
On the other hand, if by chance you are using fresh water onboard through a direct dock connection, then you have an unlimited fresh water supply, so a leak anywhere in the circuit can in the worst case sink the boat at the dock, if the bilge pump doesn't work or can't keep up with the flow.

You should really avoid connecting to shore water unless you are on board and turn it off when you leave. Personally I have never connected any boat to shore water. Also, using tank water ensures the water stays fresh. In most places city water contain chlorine which helps clean your tanks

small boat builders have a bad habit of installing undersized pumps. Don’t count on a 1200GHP pump to be able to keep up with a shore water leak or anything more than a trickle

Happy to have helped.
Just a couple of further comments:

Actually, there's nothing wrong in closing sea water intakes when not used.
The one you found must be either for a main engine or a genset cooling, so whenever you are not running them, keeping the respective sea water intakes closed is not a bad habit.
But only as long as you remember to open them again before turning the engine or genset on, otherwise you would damage them.
Or even set the boat on fire eventually, in the worst case!

Wow. Shame that we are literally an ocean apart, I would have been happy to have a look for a beer...!

PS: ref. shore water connection, personally I'm not as concerned as Pascal is.
In fact, I live aboard for 6+ months/year, and that's what I use 90% of the time.
But I also can count on a 200 psi tested fresh water circuit, multiple w/tight compartments, adequate and redundant pumps in each of them, alarms, etc.
If you are unsure of how reliable your system is, you'd better be a bit careful.

Dozens of boats sink or are badly flooded every year by shore water. Indeed it s not much of a concern on a fairly new and larger boat with good plumbing but I woudl never connect a 35 year old carver. And who knows what previous owners have butchered. When I bought my boat years ago, the solid copper plumbing was excellent except for a hose clamped on copper some genius had used for an aft deck wet bar. Popped out soon after I upgraded the fresh water pump, luckily it was outside ...