Oh there's loads. First of all her single comment is very short which sets a certain tone itself. There is absolutely 0 effort in her comment to establish a friendly tone. That itself might not necessarily mean that it reads negatively, but it will certainly not ready positively either, which is the first problem.
Secondly she says that transgender is not a gender, but she doesn't provide any constructive feedback or improvement with it. She could have explained what transgender means, or linked to a website which explains the topic well, or at least offered something along the lines "hey I happen to know a lot about this topic and would love to help you phrasing this question. Feel free to reach out to me on Slack with any questions or if you need more advice.".
"If you want to know if a survey respondent is transgender, you need to explicitly ask that question". That sentence alone comes across very much top-down as in "omg you're so stupid and don't even know what that is and you should do this or that if you want".
This is certainly not the message and tone that you want to say to someone the very first time you communicate with someone, unless you obviously don't care about how you come across, how other people feel and how it might affect them, which is fine, but then don't be surprised if people think you are unfriendly, not pleasant to work with and toxic.
For instance, if I know a lot about a programming topic and I would review someone's work for the first time I would not just say "Hey dude, what you've done here is wrong. If you want to do it right do it right man."
First I would avoid to say wrong at all and say that I think it can be improved, because my goal is to improve things and not tell people if they are right or wrong, I don't gain anything from that. Further I would offer constructive suggestions on how it can be improved and also provide extra material/links for them to educate more on that topic, because I would want them to get better and not just me look superior to them.
