I wouldn't let my guard down. He's probably having a moment of clarity. Some of them do this and length of time for clarity can vary. Maybe the depression has lifted just a wee bit to allow him to act normal, but who knows.

I would continue to observe and if he is friendly towards you, then do the same w/him, but keep those expectations at zero if you can.

Sit quietly, the answers will reveal themselves when you least expect them to.
The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.