Of course, if you incriminate yourself while spouting off (or while engaged in any other activity, like writing in your diary), then you are producing evidence of a different crime, but spouting off is not a crime in itself.
like I can say what I want, but if I say "I DID CRIMES" then guess what.. that could be used as evidence that I DID CRIMES
“Spouting off” is an idiom that can also mean “speaking without a filter” and that’s what OP meant in this case.