Let me give more detail
I was taught in school some aztec festivities involved making "pozole" (a kind of corn soup) with the meat of one sacrificed person, which was later given to everyone in the city
However, I've always had a couple of issues with this story. One is that thousands of people would want to eat from this sacred soup, so one person wouldn't be enough, you'd have to kill and prepare a ton of people, and now you run into the problem of time. You'd need to work full time for a day or two to prepare that much meat and that much soup
This all leads me to believe that while there may be a kernel of truth in this story, the reality was vastly different
Did this ritual really exist? And if it did, how was it actually practiced? What was the symbolism behind it?
You are right to be sceptical. Accusations of cannibalism are common when dealing with indigenous people, and the Mexica get the worst of it. The idea that human flesh was served with pozole is a common one, and I've seen it stated on some food blogs here and there. However, I know of no definitive evidence indicating that pozole was ever served with human flesh.
What they are referring to is tlacatlaolli. Tlacatlaolli is another type of maize stew, and its relationship to pozole is unknown. Book 2 of the Florentine Codex describes that the flesh of a sacrificial victim was placed on a bowl of tlacatlaolli and served to the captors of the victim. Somethings to note, this was not necessarily the way tlacatoalli was normally served. This occurred only during the festival of Tlacaxipehualiztli. Furthermore, only the captors family was involved, and therefore was limited to a very small segment of the population. According to Diego Duran, around 60 people were sacrificed during this festival. Exactly how many people actually ate this stew therefore is not easy to determine, but couldn't have been more than a few hundred.
Book 9 of the Florentine Codex also includes a brief mention of cannibalism. In this case, bathed slaves, that is slaves offered for sacrifice by the merchant class, were offered to Huitzilopochtli. After the sacrifice the bodies of the victims were handed back to the merchants, who cooked the remains in an olla. In a separate olla, they cooked maize stew, which they then served a piece of human flesh on, just like in Tlacaxipehualiztli. Again, it is not clear if this stew is actually pozole, or something else. Again, as with Tlacaxipehualiztli, this flesh was only eaten by a small group of people, in this case merchants, was not a widespread practice, and does not represent the normal way in which maize stews were eaten.
Sources: Durán, Diego 1971 Book of Gods and Rites and the Ancient Calendar. Translated and edited by Fernando Horcasitas, and Doris Heyden. University of Oklahoma Press, Norman.
Sahagún, Bernardino de 1959 General History of the Things of New Spain Book 9: The Merchants. Translated by Arthur O. J. Anderson, and Charles E. Dibble. University of Utah, Santa Fe. 1981 General History of the Things of New Spain Book 2: The Ceremonies. Translated by Arthur O. J. Anderson, and Charles E. Dibble. University of Utah, Santa Fe.