That was definitely different than running into a darker version of himself from a future timeline, but in a way, Peter from that time wasn't exactly as forgiving as the Petrelli sitting next to her was. If it hadn't been for her own fear of it, something nearly radiating in waves by now given the tone of conversation, he may have not been worried. He had healing abilities if she left his head on and spine connected enough; he could bend time if he saw it coming and avoid it the second time around; and hell, it wasn't like they couldn't throw down like a couple of Hulks minus the green skin and purple pants. It wasn't much of a concern... not outside of what it was doing to Niki.
While he opened his mouth to say something, who knew whether that was a good idea with that third person in the cab. He did, however, keep those brainwaves open to whatever thoughts might have been going through her mind - be they Niki's own or those belonging to Jessica.
"It's okay," he finally said, reaching out to give her hand and small, comforting squeeze, "I'll leave it at that: It's okay." Hopefully his eyes and tone of voice only assured it, not at all scared of this Jessica aside from the unpredictability in when she showed up.