I just checked the projects too and in addition to what Christian said, the reason why the other project wasn't clipping was that the level of the music/ drums you were compressing was a lot lower than the other project and combined with the way you had set your limiter and output 1-2 channel fader up, meant that it wasn't clipping.
The important thing to note, is that the volume fader on your output/ master channel adjusts the volume AFTER your limiter and other effects. Therefore, if you set your limiter up with a threshold limit of 0db.... the limiter will not let any sound over that limit. If you then add a 2db boost via your fader over and above what is coming out of your limiter, you will introduce clipping.
To begin with, always leave your output fader at 0.0db. Balance the output volume of your tracks via the instrument channels and busses.
Hope that makes sense.