unprofessional business

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This really isn't a controversial topic but I want yalls opinions. Today my old manager from a job I got fired from texted me about coming back. I got fired because they said I didn't have enough experience and they wanted to hire more experienced people. Here's what he said. 
First and foremost I thought this was a very unprofessional way of going about a job offer. 
Secondly I think he only reached out to me because I got a job at one of their competitors. When I got interview for my new job they asked me why I no longer worked at my old job and the manager tells me that what I said made no sense. So I believe they called them to confirm what I said. Then coincidentally I get a text from my old assistant manager. 
I really don't understand this. Did he really think this was professional? Did he even care that it wasn't professional? What would you have said to this?