Let us see what the rude or abusive flag means.
A reasonable person would find this content inappropriate for respectful discourse.
I think that
agpyeghrujdsg
is inappropriate discourse in general (at least I wouldn'twould not start a conversation about it), so it is also inappropriate for respectful discourse. Hence this flag can be used fofor such answer.
Also, it is abusive since the post of such "answer" is abusing the system.
However, be careful with using this flag when the user has more than 1 rep or if the user has other, non-gibberish posts. It could be a mistake, e.g. a real cat on the keyboard, and then the -100 penalty is way too severe. However, this is extremely rare.
It is not spam. Use the spam flag only if a question isis promoting services or if an answer is promoting services is a spammy way.