Huh, that used to happen to me sometimes when making posts here, but to be honest, it hasn't in awhile. Did you type something up, preview it a few times, then leave it for awhile, then go back to it, then try to post it? I feel like that's probably what caused it to happen for me.
I found that copying what I'd written and then pasting it into a new comment box fixed it and didn't register it as spam anymore. Which durrr is kind of an obvious work around for me to mention but yeah.