It isn't offensive (and probably is unfairly downvoted), but it shows a lack of research. The purpose of Haiku is an open source reimplementation of BeOS 5, so naturally the windowing UI looks just like BeOS [1]. There's a reason Haiku looks the way it does.

It's a bit of a stretch, but you could argue the comment goes against this guideline:

"Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

[1] http://lowendmac.com/2001/user-interface-mac-vs-beos/