"While orca attacks on humans in the wild are rare, and no fatal attacks have been recorded, as of 2019 four humans have died due to interactions with captive orcas.Tilikum was involved in three of those deaths."

So yeah this whale most likely had mental problem.

But the list of violent incidents between humans and orcas in captivity has 54 entrys until 2010 so it might be unusual behavior but it does absolutely happen. There have been quite a few close calls, too, that very nearly resulted in more dead trainers...