You do not need perfect pitch to quickly learn fiddle tunes by ear (source: I play fiddle, can quickly learn by ear, do not have perfect pitch). You learn tunes primarily by relative pitch, which most people can develop.

There's also an element of violin-specific pitch detection; if you play violin for long enough, you can recognize the specific timbre of different notes on a violin (particularly easy for open strings) which helps ground you while listening to a tune.