What does it mean when a guy says he will call you later after a date?

If he calls you within the next day or 2, then he likes you and was being straightforward when saying he'd call you later. No hidden message, there.

Unless you really are familiar with the person, when someone says 'later', it is not a commitment to a time frame of, if or when you will hear from them, and it's usually a nice way of saying, Good-bye.