Your spelling is correct. Deliberately staying off the pitch , yes I would agree and the goal should stand.
On angles I've seen the original shot was doubtful if it was going in and if it was deflected in why wasn't the goal given to the player who deflected into the net.
So if Blind slides off the pitch , smashes into the advertising hoardings, two metres, five metres or 20 metres behind the goal line and lies injured, the referee hasn't given permission for him to leave the field, won't stop the game because he is not 'interfering with play' -the irony- or seriously injured enough then Blind is effectively playing everyone onside. On the other hand he presumably cannot receive treatment either. And he is been injured by an outside force not on the field of play.
The referee then effectively has to say ' I give you permission to smash into the advertising hoardings'
If this is the rule, which it seems to be, although few people are aware of, then it is totally absurd and should be changed