If you put the two together it makes sense. She is force sensitive but no Jedi caliber. Someone like that might be eccentric enough to collect things related to the Jedi. A flag from Anakin’s childhood, his light saber lost (but somehow found) on Bespin. Such things are collectible items in the real world so I can see having a character acquire such thing in the Star Wars world. I don’t think Maz having these things is random. And she knows Han so she probably got him to give her all the details he knew about the Skywalkers. And when you read a fair amount of history, some things like this really do happen. So putting it in a work of fiction does not stretch credibility. If you think it does you don’t have much of an imagination.