On the other hand, dwarves were living on the plains along the rivers of what would become Kislev for thousands of years during the Golden Age with no contact.
Overall it does seem a bit hard to reconcile the whole thing, another aspect though is we do know in Divided Loyalties canon there was some disagreement in views even with the Norse dwarves that caused them to split off even before contact was lost, so a mix between not expecting there to be anyone to see, and not wanting to interact with them even if they were there (an attitude that perhaps softened on both sides over the millennia leading to the positive reaction when contact did end up being made, but before then the status quo of not bothering was firmly set) can maybe explain the lack of exploration attempts from each side.