This is what I gather;
There is an allegation against Christ Jesus if He ever taught worshipping 3 GODS to Christians. HE NEVER DID. Allah/Muhammad did not know this...
This is truly one of the great tragedies of the Mary "Theotokos" theology: "venerating" Mary as the "Mother of God", offering up prayers to her and bowing before her statue. Apparently Muhammad came into contact with Christians who were, in his eyes, worshiping Mary as a god. Thus, the "prophet" of Allah assumed that Holy Trinity was God the Father (Allah), Jesus the Son and Mary the Mother. Clearly, the Muhammedans perceived Christians as polytheistic.
You don't have to read the Koran for long to realize that Mohammed had a very distorted view of the Gospel. As an illiterate caravan merchant himself, it's plainly apparent that he never read it.
Sometimes Christians accuse the Roman Catholics of worshipping many gods, while they claim they do not. (Mary and the saints come to mind) Christians worship a trinity, which is all part of the same God. That trinity consists of God, Jesus and the Holy Spirity. To an outsider, it very much appears that they are a polytheistic bunch.
As an OUTSIDER, Allah/Muhammad who does not know the Word of God or what Christianity really believes would claim that the Trinity is polytheistic. Muhammad's OWN WORDS (or so he alleged his god "revealed" to him thus making a double whammy on himself and his god) describes the Trinity in a polytheistic way yet this IS NOT what the Bible says nor what Christians believe. If an atheist friend of mine who has researched the Bible and agrees that the Trinity IS NOT a polytheistic belief then how be it that the alleged "Seal of the prophets" could make a blundering statement equivalent to that of anyone who has never read the Bible nor understood Christianity? Simple - ILLITERACY, IGNORANCE and IMAGINATION.
When you go to a church, you don't see an altar for three gods now, do you? And neither do you find in Scripture that there are three gods now, do you? So just because you see your kid blowing smoke does that mean he is smoking? No, you first examine your kid and know the Truth of the matter. This is enough proof that Muhammad was an OUTSIDER.