I feel like Maya, and Josy, presumed that she was lesbian simply because she had an attraction to Josy that she had never displayed or expressed towards guys. She may also have not expressed much interest towards other girls either, but for her, Josy, and even Derek, her feelings towards Josy were enough for her to be considered a lesbian.
This is what I feel Maya is wanting to figure out because she had convinced herself that she was lesbian and now is not so sure. She did mention to the MC in ep 3 that she had gone out with a couple of guys before but there was nothing there, and maybe she only feels this way for the MC because she was in need of comfort and support at that time which he provided, or maybe it's that old trope that she simply hadn't met the right guy. It doesn't necessarily mean that she's hetero, but could mean she's bisexual but simply didn't know it, and this is what she feels she needs to figure out.
She certainly has an emotional attraction to the MC but it's also physical too as she, like many others, seems very enamoured with the baseball bat and has even called it "beautiful", so she's clearly not dick-averse like you might expect a full-on lesbian to be.