After your comment i was able to read it both ways. Though, i find DrHyde's comment unhelpful, and would likely downvote it myself.
"since all girls like flowers, it must have been a girl".
By the words "i assume" he did not mean "all girls" or "must have", and instead made an assumption based on the mental image of femininity, which he explained. This falls very much in line with the Jungian psychology (females associate with the Anima, males with the Animus). In which case, there is nothing wrong with the prejudging, as there is no action taken upon it.
I do see a different problem, however. If the requester was indeed male, who is also politically-incorrectly prejudiced, he might take it as an insult to be assumed to be female. Though, i'm not sure if i truly care at that point. :)