I'm sorry, but that is utter rubbish. Byzantium did and would have continued to do perfectly well as a conservator of Classical learning. In fact, given the attitudes of even the best of the Muslim diadochs towards the plundered patrimony of Greece and Rome, crediting Islam as such as 'preserving the wisdom' - or crediting Islam as such for influencing, or indeed not hindering, further developments - or claiming that it was the 'indispensable link' (and no other would do) between Classical learning and the Renascence, is like crediting the magpie with having manufactured the shiny bits it pilfers to adorn its nest.