The rules are written in a way that allows for interpretation. If the rule makers wanted it to be clear cut, then they could make it that any tyre-to-line contact was "crossing". Or that having the outermost part of the tyre vertically overlie a plane in the middle of the painted line was crossing, or various other scenarios.
I interpret it that they "crossed" the line in the same way that drivers cut corners but haven't left the track. I don't think they really gained significantly (not speaking as a RB fan), so it's a question of whether to penalise for the letter of the law being broken if that's the case.
As always, we just want consistency and it's always lacking. And they appear to have failed to account for other events that had a greater impact on the final race order, what can you do