This is one of numerous "faux-amis" that are so tricky for native French speakers. While "fameux" has the meaning an English speaker would expect, "Infâme" means odious. Other examples include "éventuellement" that means possibly (and not surely in the future), "actuellement" which translates as "nowadays" (and not really) etc.

It may be chauvinism, but etymological and geographical clues let be believe that most of these are french words that have been imported into English and whose meanings changed radically. Admittedly, some probably share a common latin origin and were declined into similar words but retaining a different subset of their original meanings.

It is often a source of weird misunderstandings between native French and English speakers, neither of which are famous for their mastery at learning foreign languages...