I agree with Owlman. It's a standard adjective here in the U.S. It's not slang or recent or anything like that.
Somebody who is unreliable in making commitments might be described as squirrelly.
Example:
You're at a family event and everybody is there except Uncle Joe. One person says, "Have you seen Uncle Joe? He promised he'd be here this time." Someone replies, "You know how squirrelly Uncle Joe can be about stuff like this. Maybe he'll show up later."
It doesn't have a specific meaning but indicates someone who doesn't act in reliable, standard predictable ways - which in different situations could be odd or silly or foolish. (Just like squirrels have erratic, irregular movements.)
Here's an example from a Google search, using it in a phrase that's a fairly common way of using it.
"Now that you’re staying put for more than one week, maybe you can meet someone, too."
That got his attention. "Geez, Adam. Don’t go all squirrelly on me. I’m glad for you two, but now is not the right time in my life to go looking for anyone."
I'm not sure of the exact intended meaning in this context because I only read this very short excerpt.