Maybe they thought, oh, she is much more qualified than this other guy. But there is just something my gut is telling me about this guy... Or for some reason, I just feel more comfortable around this guy... Or, I'm going to invest in this guy because he reminds me of myself when I was starting out.
Sure, maybe. Or maybe he knew the other founder better and was more certain of his ability to execute well. It's impossible to say exactly what weightings of factors went into his decision making. His heart of hearts is unknown to all of us (even including himself, to some extent).
Even if it were a case of unconscious bias, though, that doesn't mean she should be on Twitter accusing of him of committing collective violence against women of color by choosing to fund a white guy instead of her.
In other words, unconscious bias.