So storing the diagonal as a matrix and the new bases is more compact?
But if they read your paper enough that they invited you to a talk, that probably means they were far enough along to independently inventing it they were going to do so anyway, and wanted to chat with someone who was also doing the thing they were already doing. Good ideas tend to reveal themselves to anyone who is aware of the problem.
That's more than a stretch. They likely invited them because someone thought the abstract sounded interesting, or something like that.