The author (cc'd) says that there's no RL engine in Thea - it's quite possible that Vangelis' engine did not exist when Jesus wrote the paper.. or maybe we just need to make it more prominent!
The paper has a nice detailed description of the algorithm used (which we lack in Thea!). But from a cursory reading they sound similar. The paper describes an implementation directly over triples, whereas Thea works over OWL2 facts. I wonder if this makes a difference to performance. It would be interesting to compare the two.
Perhaps we could combine Jesus' lib (with permission) into Thea and give users a choice - although moving forward it may make sense to have a single RL implementation for SWI if they're using essentially the same forward chaining algorithm.
Cheers
Chris