I think the Sheriff's Dept reply is well done. If anything, I'm surprised they didn't simply ignore the inquiry. For the sake of a web blog like this, if you weren't there, you just can't know for certain what happened. Here is the best I can observe from this limited info.
The OP is stating that his crew didn't know where the valves were. This isn't relevant to compliance and causes me to wonder why he is trying to oversell his case.
Assuming FL has similar requirement to anywhere else I've been with these laws, it isn't simply enough to turn the valve. It must be secured, locked, handle removed, etc to comply. I suspect he knew that too, but didn't admit it.
Police officers make mistakes. However, for the very few they make, they are accused of thousands more. As a generality, pulling your weapon is as much a liability as protection and an officer typically won't do it unless absolutely necessary. They are highly trained, scared straight you might say, in the consequences of improperly discharging a weapon. That can only happen while out of the holster. Again, mistakes are made.
So no, I can't know this wasn't one of the few bad mistakes or over reactions. The odds are that the crew did something that the officer legitimately assessed could become a threat. Whether it was or not, is not the standard. He/she has the right to ensure they return home to their family from a job checking for poopy in the river. That would be a pretty lousy mission to die over.