I don't have an deep source on this, but it looks like this is not something new. https://www.etymonline.com/word/milk https://www.etymonline.com/word/milk says

I don't have an deep source on this, but it looks like this is not something new. https://www.etymonline.com/word/milk https://www.etymonline.com/word/milk says: > Of milk-like plant juices or saps from c. 1200.