I'm not imagining 'deployed' as the desert, and I'm well aware that we use civilians on the daily for target practice. Hell, I've done urban E&E myself. It's great training, and it's needed. There's a reason it's not readily disclosed how and where we practice with military skill sets. Civilians simply wouldn't understand. However, being on the business end of an ISR lens, bombsight, empty barrel, or HUD is one thing. Doing practice interrogations in public lodging is something completely different.
The deployed locations that mirror a major US city where DoD would need these skills are many and varied. We definitely need to train for that. That's why we have secure facilities specifically built for the purpose of replicating those environments (with obvious limitations). There are times when a major US city is the only place to practice employment, tradecraft, etc. But, practice interrogation should not be happening in a civilian environment for the exact reason that they hit the wrong target and didn't immediately realize it. That's all kinds of unsat. Interrogation...as in get information. If they are brand new to this, it should happen in a controlled environment. If they aren't new, the instructors should be fired. It should have taken all of 5 seconds for the instructors to realize they had the wrong dude/wrong room. Field interrogation is one of the few times we question someone without knowing much about them. I get this guy probably just sat in a tub while an academic situation was occurring, but that is precisely why this kind of training should never happen in a civilian environment.
FBI training DoD, I get it. There's nothing wrong there. But they HAVE to weigh the risks of making a mistake like this though. It really does make them look like the gestapo, especially in today's social and political environment. Hitting the wrong target in a person-to-person environment, possibly even disclosing some ways and means, speaks to a serious problem in the system. Risk vs reward analysis is way off somewhere in that training process. I sincerely hope this isn't an indicator of the proficiency levels in our federal agencies.
That all assumes this was actually a training event. I'm not willing to discount that it could have actually been a real event that missed it's target. "Training event" would be a likely cover story for such a miss. That's no conspiracy, just a statement of fact. We can't be immune to the fact that this is precisely how federal agencies interdict bad guys. All the more need for well planned training.
Either way, I think you're right: that dude's getting paid.