I had those same small red bites/dots covering a good portion of one of my lower legs following a recent FRA-DFW flight. I didn't notice it until I got home. I actually thought it was from the hotel where I stayed at (or a public lobby). Unless you have actual proof (photos or FA witness) it is very difficult to pinpoint where the bites occurred. I wouldn't notify AA and would start packing tea tree oil on your trips. It does wonders on bites and inflammation.