I figure they just stroked it - but I'm not the engineer here.
The stroker kits I've seen for the 6.2L are all around 6.6L or ~402ci. I've heard that's about the maximum for a production 6.2l Boss block before you start to run into issues. Even with that bored .60 over you're only talking about ~415ci at most.
At 460ci, I'm sure this engine has a pretty extreme stroke and bore increase.