What you're seeing here is the frequency that the dealer gets a 20 when they have a 10 card up. The simulation is 400 million rounds. Notice that 40 million times? That's almost 3 times the number of 19s, 18s or 17s. Matter of fact it is more than 17-19 combined. Dealer 20s are by far the most frequent single hand the the dealer gets. That face up 10 is deadly indeed.
In terms of parent, the dealer gets a 20 10% of the time that a 10 is showing, that's 3x more than any other hand over 16.