Please stop trying to be "nice" or "friendly". It's actually just being passive... and it looks like he's just playing with you, to see if he still has any control. Which it seems he does... maybe a little less control than before... but he still has it (maybe that answers your "why" question)
You shouldn't be worried about how you came across to him, if your message sounded like you actually wanted to talk to him. You can't save him. He can only save himself. And only you can save yourself. So, my advice would be to stop ALL contact.
I have a sort of similar experience actually... early this year my phone showed me they had called. I was shocked, thrown off guard for a bit... wondering and wondering "why did they call?!?" I missed them. But I also knew how controlling and manipulative they were. So I didn't call back. Then, a couple months ago, they sent me a FB message, again, totally out of the blue. Just a regular, normal message. So, I marked it unread, and never responded. I just can't. Wow, now that I think of it, they also showed up unannounced on my front step, this summer. I guess they were getting desperate. I spent the day with them. And things felt like normal. The good, and the bad... I noticed that the bad really was bad, though. I knew if I would have seen them again, they would have started in on all their abusive stuff.... it happens so insidiously, you don't always realise it until it's too late. So, my decision since then has been to never ever talk to them again. Period. They never changed. I really thought they might have - but they didn't. And I can't make them. They just pretend to change.
Anyway, sorry about that. I just think you're being passive, and opening the door for hurt. Why don't you be kind to yourself, and stay away from this person? I don't know the whole story, but my gut tells me this is not good.