Kuzan joining Blackbeard wasn't publicly known at that point, only rumors were spreading in the underworld, with Aokiji traveling more solo(or rather with Camel), hence Smoker's and Doffy's speculations surrounding the rumors, and Burgess'-Teach's discussion resolving around whether they should trust Aokiji or not in dressrosa(with Teach saying it's just like with Shiryu).
It's possible the confirmation only came later, with Kuzan actively working for Blackbeard(probably a mission of trust decided by Blackbeard) by going to WCI to steal poneglyph copy, disable the remaining enemies of the crew and capture Pudding. It's probably after that raid that it became clear to the world government that Kuzan is indeed working for Blackbeard, potentially explaining his bounty increase
It's also the only event that could make sense now that, that cover story is tied with the current events of Pudding captured in Blackbeard's ship(with Aokiji and Van in the ship), all ready to get another poneglyph copy from Law