I don't think the ATC is at fault here. If they were put in a difficult situation and responsible for too much at once, I'd view that as a leadership bug, not their personal fault (or anything they should be held liable for). The weak links imo here are the firetruck driver and whoever that ATC reports to directly (i.e., there shouldn't have been an opportunity for this to happen—that's an executive failure, whether they want to take ownership or not).

The weak link is the system in place which puts so much work on so few staff.

The fire truck received the go ahead. They weigh 3x more than a normal firetruck. They're rushing to a different emergency. The plane is moving fast as hell. They can't just react instantaneously.

The ATC worker is clearly too stretched and such an incident was an inevitability. When they're shouting stop, they are no longer directly talking to the firetruck, which obscures the situation for everyone.

It is a terrible tragedy that will only be prevented with reform in staffing and safety procedures.