Kellen didn't realise how difficult it would be to navigate not revealing his powers to others until it came to the press conference. He knew how his powers worked while the others didn't. They did, however, know how Rhys' powers worked so they couldn't just brush off everything that Kellen saw as what Rhys saw.
It wouldn't work because they knew how Rhys saw things, and knew that he wouldn't be able to see anything with Kellen in it. Not without it being something that he clawed to get. Kellen had gotten the vision rather painlessly, and it would look weird if he was the one answering all of the questions that were supposed to be directed towards Rhys.
It was annoying that Kellen couldn't reveal the new powers he had, even if he understood why he couldn't. They couldn't trust everyone in the room. While they might not be working for the E.A.G., the Invisibility Esper who had attacked him was a good example of the other dangers that being in a major city posed.
