Sounds to me like this person is just afraid of not fitting in. That was one of my concerns back when I was deciding whether to transition or not: I was afraid to transition because I thought some people would never truly see me as a man, because with the surgical options as they are, I'd decided if I transitioned I wouldn't get lower surgery. At the time, I didn't experience as much dysphoria as I soon did later on, I don't really know why but I was much better able to handle it, which is why I even considered staying "female" at all.
But ultimately, whether someone is FtM, a cis-female, or androgyne/gender-queer/etc., is a matter of personal identity: if this person identifies as FtM, then that's what he is, regardless of real or perceived femininity or of levels of dysphoria, etc.
And, as Kreuzfidel said, testosterone won't change someone's natural mannerisms. But with practice, they can change their mannerisms/the way they walk, etc., no hormones or anything else needed. It's a matter of habit. And even if those don't change, testosterone's masculinizing effects are strong enough that, with time, it won't really matter: if you see a masculine-looking man with a somewhat-feminine walk, would it make you question his gender? Nah, probably not... Cis-guys vary in their levels of masculinity, too, so it may not be as big a deal as this person thinks.
My two cents
