That's absolutely incorrect. Herms/Futas or "Hermaphrodites" are feminine bodied people who typically have both sets of genetalia. To a much broader extent, it just means any person that has both parts. Futanari is just the Japanese colloquial. This is different from being trans, and if it's being used as an "insult," it's more likely that the offender doesn't at all understand the difference. It's not derogatory, it's simply a descriptor.
It's quite annoying when it's framed like that. Same for "femboy", which are men that simply like to dress or appear as women. Literally just short for "feminine boys." They (commonly in media) aren't actually trying to be women and therefore aren't trans, and yet they are seen as such. People latched onto the word, "claimed it," and then saw it as offensive, which is so egregiously disappointing.
Honestly this digital world just seeks anger, nowadays. Ridiculous.