One theory is people thought the telegraph wires looked like the wires they use to train grapevines, so when they got a new message they'd say they heard it through the grapevine, or on the grapevine.
一种理论是,人们认为电报线看起来像他们用来牵引葡萄藤的线,所以他们得到一个新消息,他们会说他们是通过葡萄藤听到的(通过小道消息)可以用 through 或者 on。