Impressive when you realize the architectural limitations they're working against: compared to the C64, the Apple II has, in classic Apple fashion, no affordances towards multimedia (e.g. no fast RAM for video) and no meaningful special-purpose graphics/audio hardware, and this is on top of Woz's hacks. It looks like they're using timing interrupts from the Mockingboard.
Part of the humor is poking fun at that, and being awed at being able to do something recognizable at all.
Keep in mind the Apple II was designed in 1977 by a cash-strapped college dropout from off-the-shelf parts. Fast RAM for video didn’t exist. Classic Apple multimedia parsimony was a thing, but it came later.
This was the most serious constraint. Aside from the 6502 CPU, its memory, and the ROMs, everything on the original Apple II was constructed from simple, off-the-shelf logic ICs. No custom ICs besides the ROM; no highly integrated parts besides the CPU. You can still buy all the parts to build one yourself.
Later versions of the Apple II replaced increasing amounts of the discrete logic with custom ICs, but the basic principles of operation (and the limitations that came with them) remained the same.
It sort-of did have fast RAM for video! The chips used could do 2e6 bytes/second, or thereabouts, of which the CPU could demand just ~1e6 (or near enough), at predictable regular intervals. The remainder is entirely free for the video system! (This was a very common arrangement for the 6502, as it has predictable data bus accesses.)
I'm not especially familiar with the Apple II's graphics capabilities, but it sounds like all its various modes need ~1 byte/microsecond for the visible period, so this would work out.
Yeah, I had to chuckle at how cheerfully half-assed some of the bits are. No judgment, the good parts are really good and some of those scenes really are completely impossible to even approximate on the Apple II, so why not have a bit of fun with it? The equivalent of showing up to a car race wearing a cardboard box with FERRARI sharpied on it, since you know you can't win anyway.
Part of the humor is poking fun at that, and being awed at being able to do something recognizable at all.