Would you say "mash <up-arrow> several times until" or "mash <up-arrow> until"? That is, in gaming terminology, would you ever use "mash" to describe pressing a key only a single time? Or does "mash" always describe repeatedly and rapidly pressing a key?
Mash, as it did in the above context, only describes pushing a button rapidly and repeatedly. It can be used interchangably with spam, but usually implys a shorter time frame, and when using spam, you usually name the action, not the button.
To demonstrate the difference:
"After you get knocked out in punch out, mash A to get back up"
"In Quake 2, spamming rockets to protect entryways is the only use for the stupid things."