I knew Oda introducing the Seraphim using Blackbeard was important.
Blackbeard would NOT just ignore something like that, and, since they're PX units, he would know Vegapunk was making the Seraphim, since he was a Shichibukai, and saw PX Pacista Units at Marineford. Blackbeard also seemed to know that the Seraphim looked like a Lunarian:
Blackbeard also has a huge interest in history, so it would make sense for him to want Vegapunk's knowledge, especially once he learns about Ohara's info being kept with the Punks.