From the Wikipedia article:
The name derives from the chocolate truffle's similarity in appearance to truffles, a tuber fungus.[2]
Looking at the truffles (the mushroom) page, they do look similar, especially to some of the powdered styles of chocolate truffles. I imagine that confectioners also like the name because it implies high quality, high prices and a difficult process to make it, and chocolate truffles are indeed quite expensive compared to a chocolate bar.







There's also truffle dogs! They have the advantage of being less likely to eat the truffles.