My takeaway was that he was asking "why you don't kill yourself' his patients.
So finding 'meaning of the life' could be seen as reply to the question 'why don't you kill yourself?' or rather 'why do you need to live?'. Could be wife, kids, family plans etc. That what kept them alive in concentration camp was their meaning.
I also liked this book. Also because it shows how similar problems people had then.
For more stoicism I would recommend "Daily Stoic". It's one meditation per day.