
I can understand why not thinking trans man can be lesbians can be confusing, especially if you don't move past the word "man", however, there is a difference between a trans man and a cis man and that difference is rooted in being a female. Because trans men can live as a woman/girl for so long, they can have a really deep connection to lesbianhood that cis men don't have. When transitioning, trans men can still have that sapphic connection and continue to embrace that.
when using labels it's really easy to trap yourself into a box where anything outside of that is wrong. Trans man has a large umbrella of different ways they can present themselves and see themselves. Transness already breaks away from the norms of the cis society and therefore expecting them to perform masculinity and sexuality the same way cis men do is done in bad faith and limits the best part about queerness