That’s actually the dogs bed that Flash has laid claim too. However you are correct, Flash does play with the backpack straps.
My cat does this sometimes when we're on opposite ends of the hallway. Unfortunately I haven't caught it on film yet.
We had a shop cat, Sisko, a long time ago who came from a feral colony as a kitten. He did something similar where he would arch like that & run at one of us in a "sideways advancing behaviour" as a sort of challenge to get us to chase him. He wasn't that clumsy though. Right after Sisko died, my male cat did the move once, the only time he ever did anything like it. I think he was channeling Sisko.
Kaylee, my oldest, laid on my lap for the second time in two days. It's the first time she's done that in months or a year and about the same amount of time before that. She used to live on my lap when she was a kitten.