Any fermented, malted starch drink is technically a beer. Chicha which is made entirely on corn is an ancient native Americas drink; many South-East Asian countries make rice lagers or ales; authentic ginger beer ferments raw sugars and ginger; gluten-free beers are often made with rice, sorghum, quinoa or other non-wheat and non-barley grains. There’s a plethora of different beers out there made with very different ingredients that all share the same brewing process.

So, yes, as long as you were able to malt the sweet potato to induce sugars that you then ferment using yeast without distillation, you’re producing beer.