From what I see posted here, it sure seems to me like they are filling the niche that Thamnophis, Nerodia, Natrix, etc fill in Europe and the US, rather than being a rat snack with slightly peculiar tendencies. Especially the fact that they seem resistant to take pinkies unless being scented, just doesn't seem right for an animal that is essentially a rat snake.

But the interesting question would be whether they are more closely related to Nerodia and Thamnophis, or is it just an example of convergent evolution.