I am not surprised that hormones work one way on our brains and another on cis brains, because it's apples and oranges. If you give testosterone to a gay man, his brain already is on testosterone, so why would it make any difference for him?
There are both lesbian trans and cis women, so there must be more to it that estrogen makes you always be attracted to men. I think this idea that a lot of us find our orientation shifting has more to do with the new clarity that comes with coming out of denial. Barriers fall away, smoke clears, and suddenly you make different conclusions about the makeup of your reality.
Regarding the studies, it is early days, so you can't really draw any concrete conclusions about what they have found, but just in case you are curious, they have done different kinds of studies on both pre and post HRT brains and have found very similar things. Our brains appear to be structurally different from cis male brains. These are studies that have been peer reviewed and most of them I believe have been repeated by other labs, so it seems to be good science. I think there are both potentially good and bad implications, but we will have to wait to see, because it is so early in the process. I think whatever the case, we should never mistrust knowledge. The minute you start doing that is the minute you start diverging from the truth and into lala land.