That would be my guess, but who knows. I've never seen the term "music
port" used.
If the boombox has phone jacks, then it's more likely line in. But
perhaps it's to conenct an MP3 player, in which case it might be USB, or
some connector specific to something like the iPod. There's equipment now
that has a USB port so you can attach a flash drive, and inside the
equipment is the circuitry to play MP3s off the drive. So that's another
possibility.
Michael