Calqued “hot dog” (热狗) with transliterated “doughnut” (多拿滋), which is like “lots of - get - (to) grow/nourish” if you attempt to parse it as a real Chinese word (character meanings often influence the specific transliteration). The “zī” character (滋) is also used phonetically in the transliteration of AIDS (艾滋病), which is the connection, but I still can’t really see how this happened.