Looks way low to me.
I can get nearly that much out of one of my small model engines with a cheap coin size generator.
A big engine like that should be able to produce much more.
Most likely they are using an automotive alternator or other generator that requires very high RPM to work at all, never mind efficiently.
That is exactly the same engine as my KyKo fan engine. I haven't run any tests but probably could if you want.
I do know from experience though, you need at least about a 5 hp engine geared up a lot for high enough RPM to get
anything out of a typical car or truck alternator.
Looks like that generator is actually geared down.
It also looks like they have four timing marks on the generator pulley, which would quadruple the actual RPM.
Hard to say why anyone would do that. Maybe a strobe effect?
Also I don't know, but the RPM seems too high. Maybe the motor is turning the engine?
My KyKo fan runs at a very leisurely RPM with no load, just fan blades. Seems odd to me.