I need thoughts and opinions. Flirting or not flirting? interested in something or not?

We’re close in age & worked together almost a year. Things have always been friendly and cordial between us, just casual convos and smiles in passing. out of nowhere he’s extra chatty and hanging around more, & seems to be laughing hard at my jokes. He would subtly talk himself up & show off a bit. The next I saw him after that he wasn’t even looking in my direction so I chat with him first just to see and he gets all smiley with me & starts eyeing me playfully and flirtatiously on the dl, but making sure I see him. if he wasn’t flirting or putting something out there for me to pick up, I don’t think he would’ve started with the looks/eyes. This has never been the vibe between us so I don't know what changed.

I call him out for the flirting and he backs off for months to follow. I just asked if he had been flirting rather than just asking him out or flirting back & he immediately denies it and plays it off, asking if he’s being too friendly (so he was aware his behavior was different) and in defense mode I say “yeah a little.” He then says he’s just there to have a good time. He then months later, starts being chatty again which I don’t think too hard about until he points out a stray hair on my hat and brushes it off for me around other higher ups. I really wouldn’t think too much about it now but I feel like I should know better knowing how he’s been in the past with me.
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They don’t work on the same level as I do
I need thoughts and opinions. Flirting or not flirting? interested in something or not?
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