I do remember that thread/post. It reminded me why I like you.
Now an unsolicited or uninvited or inappropriate kiss does come pretty darn close to the definition of assault. Just as bonking somebody on the head with a newspaper, slapping them for making an insulting comment, shoving them in frustration all technically constitute assault. As does even threatening such actions for that matter.
But it all depends on the the circumstances, context, and degree of harm. I can't say I wouldn't have reacted as you initially did if somebody inappropriately grabbed me and kissed me--most especially somebody I wasn't at all interested in and had never indicated I was open to dating that person or whatever. You also said you forgave that person, apologized for overreaction--I think you probably didn't over react--and you remain friends. He got the message loud and clear that such behavior was unacceptable to you. You kept a friend. That is how almost all such situations like that should end.
All unsolicited kisses are not assault however.
Consider the kissing scene in "The Devil Wears Prada". Andy Sachs was not expecting the kiss from Christian Thompson and she kept telling him why she couldn't do that and he kept kissing her until she finally 'was out of excuses' and initiated the final kiss in that scene. That kiss was not assault. I think intellectually honest people know the difference.
https://www.youtube.com/watch?v=NBqgHjpY4FU