This is incorrect. I remember when this term emerged in the early 2010s, and it was a synonym for "trap." Basically, a femboy was a guy who looked like a cis woman regardless of hairstyle, without any relation to clothing or behavior. However, starting in 2019 with its popularization, the term "femboy" began to be associated with behavior and clothing, no longer just appearance. In summary, originally a femboy was a "trans" involuntary person but didn’t need estrogen because they were naturally very feminine.
Also, I say incorrect in the sense that you think femboy is gay and trans is not, when they’re the same thing. Gay men don’t like femboys. It’s a fetish for heterosexual and predominantly straight bisexual men (kinsey scale 1). Thinking there’s a huge gap separating femboy from trans is pure madness. At least when we use the original femboy term.