The Talmud questions the formulation of the baraita, and then explains its intent.

Does it enter your mind that any father who does not teach his son a trade actually teaches him banditry? Does a father who does not teach his son a profession, teach him to rob? Rather, one should adjust the formulation slightly: With regard to a father who does not teach his son a trade, it is as though he teaches him banditry. Since the son has no profession, he is likely to seek his livelihood dishonestly.