These are 'nicknames'. Not sure how you have come to the conclusion that an accomplished violinist considers themselves 'more' special by using the nickname.
If anything, and I'm stretching here, it would be an attempt to be inclusive..."we're all fiddle players here!".
While I mostly play classical, I tend to spend the summer fiddling. I call my violin a violin. Never called it a fiddle, since that's not my main interest, but I do refer to fiddle music...but that's just me...