I don't doubt he doesn't seem to worry about a fire but if I was near his boat, I would be worried about a fire. Marina fires often hop from one boat to the next until they are all burning.
And of course. as someone else pointed out, a charcoal fire emits a lot of carbon monoxide. That might not be a concern for you but it indicates that your slip neighbor is pretty ignorant about these things.
I talked with him about the co, etc... he just thinks it is not ever a problem. It is a risk, he does have a co alarm.
I asked him what happens when the wind blows, if it still works ok, and he says yes.
Marina fires are bad, I think his stove being solidly attached is pretty safe. The fire risk would be sparks when opening the door something falls out.
What is the main causes of fires, likely they are electrical? Of course not many have wood stoves in their boats.
To me the main risk would be getting burned bumping into a stove.
I have Cruisair heat pump and 2 electric heaters. One heater pulls 7 amps, the other 10 amps. the heat pump 12 amps. I have 2 30 amp plugs. But our marine offers free power so I just use one 30 amp plug. With 2 electric heaters on, heats ok the boat.
Heat pump works in 40* water, but water in 30's, it does not heat as good. It does heat a little with water in 30's.
My boat has so much glass area, cabin heats up a lot by solar radiation. In winter can 30's outside and 60 in the boat from sun. Makes for very hot summer days in the cabin. Like yesterday, I go to boat, air temp is low 70's, cabin inside 98* in bright sun as measured by a digital thermometer located under the front forward sloping windows..
And have large twin engines in under the sole. I could run the engines and lift a hatch and a lot of heat will come in, if I was desperate for heat, which I am not.
I actually prefer cooler air, I am very happy with upper 40's, as long as it is not too humid. That humid air can make it feel real cold.