Depends on the question
The question as asked -what counts as a mag fed gun:
A gun fed by magazine
A box mag may not count - if it's a box mag build that force feeds to a tube fed into the feedneck, then that's not realy magazine fed (in my mind)
That's a force feed that allows mounting in other positions, such as qloaders, warp feeds and feedrucks
But in the good old 'what is/should be allowed at a mag fed game':
It all depends, and is up to the organiser
If the organiser wants strict magfed then that's what they mean
If they mean limited paint, then they could mean mag fed, stick feed, tac caps, or even full size hoppers and carry limits, or 50 shots per pod etc
There are more players with magfeds now, so ought he organisers want to then they can be stricter on the criteria if that's what they want
If anyone ever brings up milsim as a generic term for woodsball / scenario then I will usually pop up disputing this
But in many cases at the moment that's the arguing point on the 'what's allowed' situation - if a game is milsim magfed then that's fair enough