It's a start, but doesn't prove anything. How big are the matches? If they're tiny, it's more likely that this is just coincidence. If you look at the shared matches with each of those matches, do they overlap (match each other and maybe share other shared matches), suggesting a cluster descended from a common ancestor? Dig into the paper trail and see whether there's support for the relationships.
With that close an ancestor, you might be better off using cluster analysis to look for close (3rd-4th cousin) matches that you know aren't descended from your other great great grandparents, rather than relying on Thrulines.