No, because plagiarism is when you copy something verbatim, without creating your own authentic interpretation and expression. All art has elements of borrowing, but it's inventiveness, imagination, and some originality, that makes it art and not plagiarism.

The question is whether a machine is capable of inventiveness, imagination, originality, thinking, feeling, etc., or not, since those things have generally been acknowledged throughout history as being necessary elements of art. Wind and rain may carve patterns that are as beautiful as the most beautiful painting, but we don't call it art. Some people believe, or want to believe, that computers are capable of those things, and so we should call the patterns they produce, original, creative art. Others think that those things are not actually necessary, and we should call it art anyway. Personally, I think it's neither art nor plagiarism, but something else, that we don't have words for yet, and we're not sure how to deal with. It's a necessary discussion to work it out, but trying to fit dramatically new things into old categories is usually less successful than creating new categories.