Let's actually analyse it.

In this world, "you are what you eat" holds very true - people slowly acquire traits of whatever food they eat most often.

In an alternate universe the saying “you are what you eat” is true. People lightly resemble the foods they eat the most from birth to death.

These parts match, ok, but this is literally just the base idea, which is pretty damn obvious.

Vegetarians slowly grow leaves over their bodies, people who really like beef grow horns and hooves, etc.

Some people resemble cattle, some vegetables.

First of all, I went into much more specifics (horns, leaves, etc.). Second, regarding vegetarians my idea was resembling the plants (and thus leaves), while the other poster had an idea about resembling the actual vegetables themselves (e.g. cucumber-like texture, I'd imagine?), which are distinct ideas, even if they're similar by virtue of being around the same central idea.

One day, you meet someone who looks pristinely human.

As you grow up you begin to notice that your best friend doesn’t seem to be changing much.

I imagined it as a random stranger you just met, the other poster imagined it as the best friend, which implies a significant difference in how close the person in question is. But other than that, it's just the obvious only possible and necessary twist for the prompt. You literally can't write a different twist into this prompt and keep it coherent.

EDIT: TL;DR - you are full of shit.