Is it possible for other infections to show as chlamydia on test results for a male, who has not been sexually active for a lengthy period of time?

Chlamydia: Nope. But, the secret about chlamydia is that it can live for years silently in a male without symptoms.

Not likely: Depending on the type of chlamydia test he had, they are generally highly accurate. It's more likely that he has an old infection that has not been bothering him for a long time. Men can harbor this infection without symptoms indefinitely.