There's a difference between rot and Brot, although out of context you're more likely to misinterpret it due to the robo-voice.
The sentence 'Er isst Rot' is rather nonsensical and unlikely to be accepted as an alternative answer. You can eat many things that are red-coloured, but you cannot eat the colour itself.
When the sentences with isst sound so confusing, that's probably a hint that you should consider that it's actually ist instead. The two words sound exactly the same, but Er ist rot makes much more sense.
While "he" could be red, for example because he is sunburnt, it is more likely that this sentence should be translated as "It is red". German uses the gendered pronouns to refer to inanimate objects, unlike English. So for example you could have the following conversation:
Welche Farbe hat deinen Wagen? = "Which colour is your car?"
Er ist rot = "It is red"