The last few Super Bowls have been decidedly partisan, with Patriots fans turning Mercedes-Benz Stadium into a home game for Super Bowl LIII and Eagles fans overtaking the Twin Cities for Super Bowl LII. It makes sense that Chiefs fans would outnumber 49ers fans, as Miami is closer to Kansas City than San Francisco, so it could be accessibly by plane or in a lengthy road trip, and the Chiefs have a 50-year Super Bowl drought, whereas the Niners were just in the big game seven years ago.
48 was full of Bronco fans and the Broncos got WHUPPED. So I don't think the crowd is going to factor into this one bit.
The Niners won a shootout in the SuperDome then the ultra-crucial week 17 IN Seattle. The crowd being Chiefs heavy will make little to no difference.