In a grant application, how to address gender aspects when working in a highly technical field?

It's unclear to me what "gender aspects" means. It sounds like you're assuming it's asking about handling gender in your research, which is a great question since a lot of studies (especially psych and medical) have been done on all-male participants. Some of these fail to replicate in mixed-gender or all-woman experiments. There's also a pretty interesting (and depressing) history of abuse of women in scientific research as research subjects that has gained greater attention recently, which is wonderful. In that aspect it seems like it won't relate to your work at all, since you don't have test subjects. Even amongst research program without the kinds of testing issues, some projects in philosophy, social theory, or medicine are plagued by sexism in their experimental design or theoretical conceit. Here the issue is less the treatment of test subjects as inherent issues and assumptions in the underlying theories. This would also not apply to mathematics, physics, or computer science as they don't develop theories about humans.

However it could also mean to ask about more administrative things, like discrimination against women and transgender people in the project. If this is a small project it might not relate to you, but in a larger project and especially a in a lab this is important.

To clarify, by "small" I mean "me and two of my grad students and we know each other well." Even a working group of 5-10 people can run into gender discrimination issues. Do you know how you'd respond if a woman working under you came to you and said that she was being harassed or her ideas were being discounted because she's a woman? Do you know how you'd respond if a new grad student was to join and tell you that they were transgender? Or how you'd respond if they were rejected by other people in the project because they are transgender? If you haven't thought about these things, you definitely should. Even if this isn't what they meant, you should have an answer to these questions.

I would recommend reaching out and asking for clarification as to which of these interpretations is meant. Definitely don't say "I don't think it matters to my work" because that can come across really poorly, especially if they mean the second interpretation I gave. Simply say that you were unsure if the question was asking about gender as a topic inside of the research or about discrimination within the group of researchers.

You can try, as others suggest, "ask for clarification", but in my experience it is likely to result in a loss of time. Large funding organizations are extremely bureaucratic, and the application guidelines have likely been designed by committee consisting e. g. of a physicist, psychologist and a professor of art and letters. That committee will not convene to answer your questions, and may have nothing to do with the panel that will evaluate your proposal. So, the question "what do they mean" may not even have a well-defined answer, and even if you receive an answer, there is no guarantee that the panel evaluating your proposal will be bound to use the same interpretation.

What I would write in this case is that there is no gender issues pertaining to the research program, and then pledge to adhere to best practices in hiring and in everyday life of the research group.