alt Hacker NewsAh, but cats won't just comfortably sit on a mat if they feel there is danger. They will only sit on a mat if they feel comfortable! Absent larger context, the sentence is in fact ambiguous (though I agree your reading is the most natural and obvious one).
But do we usually describe cats as comfortable, as in their feelings? We might say he IS comfortable, or he feels comfort, but for something to be "comfortable" that implies it gives comfort to others. I can see a cat being comfortable to a human, in that a cat gives comfort to a human. But I wouldn't say "The cat is comfortable, therefore he laid on a mat." Its almost a garden path sentence, I would expect "The cat is comfortable, that's why I let him lay on me".