Well, the dude is a biblical scholar so he's doing scholarly stuff.
He's apparently more putting the Gospel of Mark more into the context of the times. He's saying Mark's audience would have understood religion in context of Roman rule. He's saying the gospel was subtly subversive to Roman rule.
Or some such.
As I also think; Jesus was “subtly subversive to Roman rule.” Maybe not so subtle at times. Mark (15:17-19) has him “chasing vendors and shoppers.” (SV)
On one hand "duh!" On the other, "not really bub."
The place were Rome and Christianity came into conflict was the same place that Rome and Judaism came into conflict, both refused to worship the state as god. However Judaism was a established religion so while the Romans often scratched their heads in puzzlement over it they mostly understood that it was nothing personal. However in the case of Christianity once it split off from Judaism and became a spreading popular religion the refusal to worship the state was seen as dangerously subversive.
He would be more correct to say that Rome saw it as subversive, not that it actually was. If Roman had still be a republic rather then a quasi-theocracy headed by a god/emperor I dare say the conflict would have been minimal.