If it works it works
Assuming it isn't just game mechanics, the Mohorovicic discontinuity (fancy word for when rock turns to magma underground) is 40-50 kilometers deep when you're on a continent
A proper timeframe can be gotten when a proper blog is made but for now, that in 5 seconds (they'd have to make the trip to and back anyways so that'd be 10 seconds which is a bit high end)
8000 meters per second, Mach 23
But it may just be them not considering the arena, since a few seconds isn't really enough time to properly heat up or gather any magma
On the other hand it's fine they just used the sheer friction to do most of the work, scraped against the magma because it's cozy, then jumped back up
(that's also a meme)
While we are here, can you get video links for the stuff you're mentioning so I can take a look at it?