I don't think you were in the wrong. It was a sweet gesture but perhaps the reason they thought it was weird is because it might come across as you trying to interfere with her relationship and weasel your way in. Of course if your intentions were pure then you're a sweet guy, if you did it with the intention to show yourself as a better prospective boyfriend then that's playing dirty and 'weird' as your colleagues put it.
I don't think you were in the wrong. It was a sweet gesture but perhaps the reason they thought it was weird is because it might come across as you trying to interfere with her relationship and weasel your way in. Of course if your intentions were pure then you're a sweet guy, if you did it with the intention to show yourself as a better prospective boyfriend then that's playing dirty and 'weird' as your colleagues put it.