Is the PhD thesis needed for a faculty appointment? I applied for a full professor position, and after the interview, I was asked for a copy of my PhD thesis.

I was confused and want to know if it is the common and normal procedure or happened for me based on a specific reason?

Because, my strong works were done after my PhD, and I didn't know that my PhD project would be used for judging me (frankly, I'm not proud of that project).
One of the general prerequisites in this day and age for a faculty appointment is an earned (as opposed to honorary) PhD from a (typically accredited) degree-granting institution. 

Consequently, asking to see either a PhD thesis, a transcript, or the degree certificate is would be ways of ascertaining that you do, in fact, have a valid degree. This by no means implies that only your PhD matters in the hiring process; just that it's part of the process to ensure you're eligible. I wouldn't read too much into this beyond that.