Fat cat is my

A student was joking about how learning Spanish was taking away from "time spent crafting my Russian translations". She added that she had had to create a sentence with "ay caramba" and, "as I only know about six words", was finding it difficult. She came up with ¡Ay caramba! ¡Mi gato es mas gordo! and added "this either means my cat is too fat or my cat is very fat, I'm not sure which. But it got me high fives from the other students. I was totally floating on cloud nueve."

Another of the Russian class suggested it meant "my cat is more fat". (This, by the way, is correct.)

According to Google translate, it just means "my cat is fat", which is what "mi gato es gordo" also means.

But why I'm posting this is that GT suggested I translate "mi gato es gordo" from Portuguese. Why not?, I figured, and clicked.

According to Google Translate, "mi gato es gordo" is Portuguese for "fat cat es mi."

Okay, I get that Portuguese isn't Spanish. ("My cat is fat" is "meu gato é gordo", in case you're wondering.) But I don't know why GT suggested I translate from a language that 50% of the words didn't belong to. And I don't get why the word order was so drastically changed.

I don't get how machine translation purports to work at all, in fact...