It's only 4 provinces in 16 turns. I suppose it would have been have been faster if you could have played you loan without removing the throne/grand market combo from the top of your deck .
I think it's hard to say by this criteria. He possibly could have gotten more if he wanted to, and his deck is certainly able to get to 6 or even 8 quite easily and rather fast. It's in general very difficult to compare engines to this BM benchmark because they work completely differnet regarding timing and reliablity.