"There's <<a cat on ,my keyboard!~" splash minor text error

Likely WAI. No punctuation would be correct between "on" and "my", since they're part of the same clause. The comma is, much like the "<<" and "~", of feline origin, and cats do not know spacing rules.

Aren't the randomly placed characters the entire joke of this splash?

yeah the whole joke is that the cat is pressing random keys and making it look all wonky

There shouldn't actually be a comma there at all. Obviously intentional.