"Call shy" birds is probably the biggest myth in turkey, hunting and behavoir. Their entire life is based on vocalization with one another. To gather, mate, announce danger, it's all they know. Why that Tom didn't play by the rules, I have know idea. Could of been a hen out of sight from you. Heading to roost as mentioned. Or maybe he boinked all day and was just tired,who knows? If they really become call shy, they cease to exist.