Both. Russian forces occupied it, but Crimea's population is over 60% Russian. While the exact referendum poll numbers could have been fabricated (95% for), most of the polls after the referendum showed 80+% support.
It was actually 100% because both of the questions asked at the referendum meant secession from Ukraine; i.e. it wasn't a simple "yes" or "no", it was essentially "secede immediately" or "do it a bit later".