It was the first time Jon shared what happened in Atlantis with anyone who didn't belong to the Mapple corporation, moreover, it was the first time he gave voice to the heart-wrenching guilt that had been eating him from the inside. Sharing his feelings in front of others was beyond difficult for him and it was only made possible by Medusa, who he considered as a daughter, being present.
Being the one who caused the arrival, Jon expected more than a few curse words thrown at him. Not only was he ready for that, but he also expected everyone in the room to lash out at him and Medusa to be really disappointed that the uncle she loved was the one who caused humanity's downfall.