It goes like this:
On Day3, during breakfast: Rowley learns from Angus that ~some polar bear~ was hitting on Welkin (and that Welkin doesn't remember anything from that).
On Day3, during lunch: Welkin tells Angus that he saw Arthur in town, but since Rowley knows the bear as Wallace, at the time, he can't connect the dots that they're in fact talking about his old friend.
On Day4: when they met in front of the hotel, Rowley is happy to see *Wallace*. He then finds out that his actual name is Arthur, and finally gets the full picture that this is the polar bear they were talking about earlier. Having that in mind, he then later in the bar starts asking Arthur questions about what actually happened between him and Welkin the last night (as Angus never told the details).