The speaker offers someone a gift of drawn flowers, and the whole poem turns on a small, painful joke: the person responds by picking them. The "then" at the end is odd. It may be a typo for "them," or it may be a deliberate break, leaving the line unfinished, as if the thought trails off. Either way, the sentence stops short, and that suits the hurt it carries.
Drawn flowers can't really be picked, so the act is either playful or careless. The person treats something made with care as if it were ordinary, something to take rather than appreciate. The speaker's feeling seems to be a quiet disappointment. They gave something imaginative and personal, and it was met with a literal, thoughtless response.
The mood is wistful and a little wry. The poem is short and plain, so the sadness comes through without any big declarations. It's the sting of making something for someone and feeling it wasn't truly seen.