The problem is understanding just how fast it affects you, and how little you need in your system. I imagine his line of thinking was "Well, if I just shout and don't breathe in, it'll be fine".
The problem is that at high enough concentrations, a single breath is all it takes. Did you remember to purge your mask before taking a breath when you put it back on?
The thing about H2S is, it's every bit as dangerous as HCN, but it has a better PR agent. If you wouldn't take off your SCBA mask in a room full of HCN, "even for just a sec," then you shouldn't do it in a room suspected of being full of H2S either.
The fire chief would have known that H2S is hazardous, but his training unfortunately (and obviously) didn't communicate just how hazardous it is.
Simple mistake to make.