They didn't come down at the same time, his toe came down first, then the heel, but a players foot being on the ground both in bounds and out of bounds at the same time will be ruled out of bounds every time regardless of what was first to touch.
As mentioned, when a runner is tiptoeing on the sideline it doesn't matter if his heel hits the ground first in bounds, if any part of that foot touches out of bounds the play is whistled dead and the call is out of bounds.
Had he had the presence of mind to not settle on his heel and lift that foot completely off the ground after his toe touched, then either fell down, or stepped completely out of bounds it would have to be ruled a catch. Similar to a WR catching the ball, hitting both feet in bounds, then stepping out of bounds.
