Sudden chicken wing??

My 5mo has JUST started doing this within the last day or two, happy or not. He’s met all the appropriate milestones so far, has incredible strength imo, showing signs of crawling soon, etc. He’s been teething terribly (gnawing on anything he can get in his mouth, flushed cheeks, watery/loose poop, general fussiness). Infants’ Tylenol and infants’ ibuprofen both help. This new movement is just kind of concerning to me bc when he’s upset, he looks like he’s hitting himself. When he’s happy/content, it just looks like he’s supposed doing the chicken dance 😂 Is this normal/common? Do I try to stop him or let him do his thing?