1 second. That was exactly how long it took for Ragnar to absorb all the information Slag had given him, remove the unnecessary parts, focus on things he thought were unimportant but actually might be, and form his own theories different from what Slag originally thought. He was quick not because the information was brief, but because his thoughts worked imperceptibly faster than normal humans.
There was one, very important thing that Slag had not realized in his assessment of the Inn. His mistake wasn't really his fault actually, it was a result of his understanding of the universe being limited.
Guessing on the possibility of there being other Inns was not something that could be done at the moment, because early conjecture without sufficient evidence would blind them to other possibilities and cause them to misinterpret new evidence to somehow fit into the narrative they thought most likely.