I’m not sure (but happy to be corrected) that there is a legal standard definition of what constitutes milk. There was a documentary on Radio 4 a few years ago that asked “What is milk?” and found that - in UK and Europe - it couldn’t be answered (other than it had some cow involvement somewhere). Some pateurised “milks” had barely any actual milk. From what I remember it was the lobbying of the dairy industry that prevented a standard definition.