Funny how you rely on a parenthesis to make your point because when a verse addresses the Holy Prophet ot uses his name or station. Anyway, this verse was revelaed after the treaty of Hubaibiya. The word that is used here signifies human weakness, not a sin. Whenever in the Quran the Prophet is promised victories he is enjoined to seek protection and forgiveness for his human weaknesses that may be stand in the way of spreading Islam. There are 4 words which have a similar connotation. The word used here has none of the sinister meaning that is applied to the other 3 words. If with this verse the Holy Prophets was declared to be sinful it would have used the other, more sinister words.
Also, relying on Western Islamic scholars is a mistake because they have nowhere near as well a knowledge of Arabic and Quranic idiom as they should. In the Quranic idiom for example, if we take the owrd used here to mean sin would mean the sins attirbuted to thee or alleged to have been committed by thee or the sins comitted against thee.
Furthermore, in the verse 5:30 where a similar word is used the meaning is the sin committed against me. So in the conext of this verse we see that, after the Treaty, all the lies and sins that were attributed to the prophet would be proven to be false because Allah would protect him from those. Moreover, the conext of this verse supports the above explanation because what is granted, a victory, has no relevance to any of it if this was meant to be sin.