I can tell you for sure on my phone (which is all I use to read/post), it's pretty easy to accidentally flag a post unintentionally. I know because I've done it. Then un-did it.
After getting the flag report I then looked at the thread in question and I have to say that DAN_M's comments were a little over the line, however I cannot see UKCMM's posts for some reason (maybe he deleted them) which may have been of an equal nature.
I would say however that making a whole separate thread just to moan about someone is a little childish.