That's crazy, but the guy probably enjoyed it. The FR4 adds a huge
thermal resistance. And those dinky leads and traces won't be happy at
600 amps.
Just buy one of these:
https://www.digikey.com/products/en?keywords=IXFH400N075T2
1000 amps peak, 1000 watts, 75 volts.
or put a few smaller fets around a heat sink, to spread out the hot
spots.
And you spent too much time watching it :-)
Reminds me of an article in Popular Electronics half a century
ago. It announced a new 1000-watt (or was it 10kW?) transistor
with a photo showing a TO-3 style case alongside a wrench that
looked tiny by comparison. Probably the April issue.