Translation:Their band played six melodies in the concert.
the correct translation for "melodie" is "song" -- what a strange concert with just six melodies...
I recently attended a violin masterclass here in Romania (I've only lived here a bit less than two months, so don't understand much of the language yet), and noticed that the verb "a cânta" was used when asking the participants to play on their violins. Is this common usage in the world of instruments, in this case stringed instruments, to use"a cânta" when referring to playing an instrument (as opposed to singing with one's voice)?
Yes, Romanian uses the same verb to describe singing and playing an instrument (eu cânt - eu cânt la vioară/ la pian/la chitară/etc.). French uses "jouer" which is similar to "to play" ( je chante - je joue du violon). Italian uses "suonare" (more or less "to sound") ( io canto - io suono il violino)