I've no idea how they asked, because I wasn't among those asked. I expect that some form-filling was done, and one of the questions was about milk alternatives. I also expect that the decision to have more milk alternatives had already been made, but this way they could spin it as responding to the needs of the customer. One person writing on a card and putting it in a suggestions box somewhere on campus is another possibility.
If only we'd asked for better-tasting coffee.