I found this person on Tumblr that I genuinely don't understand. They are agender, they used he/him/they/them '(never she/her)' pronouns and they are lesbian??? How are you he/them and lesbian, agender and he/him, and and strictly not she/her but a lesbian?? I tried asking them but they never responded. I don't mean to hate on them but I just don't get it!
Lesbian would mean that he is biologically female and attracted to the same sex. I'm sure you know what agender means...he doesn't feel either make or female and some agender people go by they/them (guessing this is the most popular), some go by he/him or she/her, he just prefers male pronouns.
Maybe he first discovered his sexuality (lesbian), then gender, but he's still mentally bound to the original sexual identity.
Technically because they're agender he can identify as a lesbian if he wishes, I don't think there's really an issue with that. I understand the confusion in regards to pronouns though as lesbians typically go by she/her. This leads me to believe that perhaps he is still accepting himself for who he is and is not yet ready to let go of his lesbian label, most likely anyway. Yes if it's a trans man that is attracted to women they would be straight, but the key difference with this person is that they stated they are agender not FtM. Although my prediction is that the way he ID's himself may change in time, but some people take a significant amount of time to adjust. Take me for example, when I discovered I was FtM I was incredibly sad to have to part with my lesbian label as it had taken me a while to become proud and comfortable with it, and the community made me feel welcome, but obviously I had to give it up eventually and did so. Ultimately though it's just a stranger you saw in passing on tumblr, I don't think it's something to really worry yourself about or fixate on.