Their scene in the street seemed like something she wasn’t expecting, and she seemed confused by what he was saying, and it seemed like it was a brief meeting and then she was alone again, and after it happened, it looked like she was reflecting on the moment and smiling. And the forehead kiss is what her father does with her, so it’d be fitting if they showed her son doing it as well.
If it was someone she had actually planned to meet, and/or someone from her past who she hadn’t seen in forever, like a long lost foster brother, I’d expect him to have been there for a longer scene where they actually spent some time catching up, but it seems that she’s left alone again rather quickly.
So AdultHenryHallucination works for me right now, judging on the pics we’ve got. But we’ve only got a handful of still photos and no actual information about the context, so it could end up being anything.