Stone gets tripped/dives whatever. He begins to fall. He doesn't want two Stars going the other way. So he tries to ensure that as he falls, he impedes Heiskanen in any way possible. He doesn't intend to hit Heisk in the knee with his head. That's stupid. But he does intend to slow him down with his falling body. This doesn't require you to believe Stone has some sort of ultra fast processing power brain. It's instinct to do this when you've played long enough.
It's a high IQ play and 99% of the time no one gets injured. You can call it reckless or dirty and I would agree but it's the type of thing that wins you games.