There do not appear to be any open wounds or signs of infections. I would say it most likely that those toes didn't fully form when the frog went through metamorphasis. It is fairly common. :-) It is also possible that the toes were bitten off by another froglet at some point. It is nothing to worry about though. I have a couple that have shortened toes. Your frog looks great. S/he justs needs a little chubbying up. :-)