Good point about the sample size. While this was the most recent study, the sample size may seem small. But yes the Non-Binary sample size is definitely small, which is why I didn't mention about them in the meme or its title.
But for your second point, it doesn't matter as much about the quantity of the sample, but the quality counts more. The University of Sydney is a very trustworthy research group. The data I'm pretty sure ended up going to the Morrison Government, but of course Scott Morrison couldn't give a stuff about wage theft.