There's always more to be said on the subject, but the responses to this question may be a good place to start: Did Pontic Steppe nomads use the friction of their horses to 'cook' meat?

With respect to the Huns, your teachers are probably thinking of the testimony of the fourth-century historian Ammianus Marcellinus, who claims in his Res Gestae that the Huns "eat the roots of wild plants and the half-raw flesh of any kind of animal whatever, which they put between their thighs and the backs of their horses, and thus warm it a little" [31.2.3]. Given that Ammianus was a contemporary of the Huns, we might expect him to be a trustworthy source, but there are a few issues that would similarly suggest we shouldn't take him at his word here: first, that he's playing into what would certainly later become (and may have already been in his time) tropes in the description of nomadic civilizations, and second, that empirical evidence suggests that saddle-cooking is downright dangerous from a food safety standpoint. For these and other reasons, most experts tend to doubt these claims (with respect to the Mongols and other steppe nomads as well as the Huns)—though with the understanding that evidence may eventually come to light to change our views once again.