The only time is becomes an issue is if you're entering it into a quilt show, even a small local one, whether judged or not.
It is both courteous and professional, and the right thing to do, to give credit to the longarm-er (is that a word?).
However, I've seen labels without it. Not so polite, but not an "arrestable" offense. Sometimes it's from Grandma to Grandbaby and, understandably, Grandma didn't feel the need to add LongarmMary to the label.:D
But you most certainly can consider yourself a quilter.