I Think maybe what he means is that there's a rear wheel from an older 5/10 speed or something. Perhaps this bike used to be a 5/10 speed or perhaps the rear wheel was trashed and someone put a random spare wheel they had on it just to make it ridable.

As others have said, we need more details. Are there one or two chain rings on the front? Is there a little metal ring on the rear dropout below/behind where the wheels axle slides in - something that looks like a rear derailleur would bolt on?