^I don't think that's quite what he said. IIRC it was more along the lines of "if it weren't for the Dark Ages we'd be colonising space by now". What happened in the Dark Ages was a massive technological regression across Europe caused (by and large) by the collapse of the Roman Empire and the final death throws of Byzantium.
While it may have been a contributing factor in a social context, the spread of Christianity in the west and Islam in the middle east and north Africa was more a symptom of that collapse than a direct cause. They were basically filling a void left by the old religions. Indeed, it was thank to the Islamic nations that a lot of Greek and Roman knowledge was preserved while we were busy burning witches and playing musical thrones (think musical chairs, but with more beheadings and less music.)
It is important to note that both Christian Europe and Islamic Middle East was built on on pagan Greek and Roman achievements as their territories covered these once pagan areas. In Islam's case, you have to include Zoroastrian Persian's culture and architecture .
For example, the dome you see on most mosque, that is actually a Zoroastrian and Byzantine architecture feature. It predates Islam by thousands of years. Russian churches have some similarities with mosques because both have Byzantine influence. The ancient Zoroastrian fire temples had huge courtyards and the Muslims copied that for their mosque design as well.
The famous crescent and star symbol is also originally an imperial Sassanid Persian symbol. When the Arabs conquered Persia in the 7th century, they adapted many aspects of the great Persian culture.
The Zoroastrian Persians also originated the concept of angels which the Jewish, Islamic and Christian mythologies later copied and modified.
As we all know that the age of enlightenment happened when we all got less religious. Religion was responsible for the Dark Ages negative effects.