It did benefit "the team against which an offence has been committed" that is if the ref never saw the handball? the ref was allowing play to continue over a penalty claim.
Should the assistant have seen the handball and informed the ref? "yes". If the assistant did then the ref decided to give a goal for reasons only he can say.
Play to the whistle and you would eliminate some of the confusion.
The thing that disgusted me about the whole thing was that when told by the ref to "Go away", the Spurs players did exactly that but then allows Rio to stand and shout at both ref and assistant whilst trying to conclude their decision. Not happy at the ref allowing the goal, Rio then continues to scream at the assistant whilst a Spurs player gets booked?
??
Arsenal done well though!!:D