Sorry but the non-union store should fire their personnel mgr for hiring the guy unless he lied about his work history on the job app. If the guy lied on that he can be fired anyway.
No sane personnel mgr should hire anyone from a union shop that quit after 19 yrs to work for half wages. That's just plain nuts!
Ya that could be a red flag, if somebody leaves a union job where he’s got better pay and benefits than he would be getting at the new job.