FIA has been very anal trying to clamp down drivers trying to use the run-off area as an advantage. e.g. Spa, Copse of Silverstone, etc...
Some might say Button push him off track, but probably all wheels off track, and power down and complete the move in the run-off area is what the stewards area.
Intend of runoff area is to avoid accidents, not to make your overtaking move.
This time the stewards have had enough.