I am sorry you are going through this, but I am certain your grandson does love you.
However, this little lad is six and trying to stand on his own feet and be a big boy. You need to accept that he does not want to be patted on the head, and I would hold my horses regarding cuddles and kisses too for a while.
Probably some other boy has told him that only babies kiss and cuddle grandma!
Anyone, child or adult, who said, "You heard me" to me, if I repeated a question I had already asked and had an answer to, would be told politely that they were being rude.
If he is saying, "You heard me" instead of answering you, point out, kindly but firmly that that is not actually an answer to the question that you just asked, and that a politely phrased question deserves an equally polite answer.
The fact that you have not seen him treating anyone else in the way he is treating you, does not necessarily mean that he isn't doing the same with others.
Don't tear yourself to pieces over this. It is a phase, that will pass.
Have you asked one of his parents if they know why this is happening? They might have an inkling, and perhaps an idea of how best to tackle it.
I myself feel that rudeness should be checked, but that no child who feels too old for physical demonstrations of affection should be forced to submit to them.
I was much his age, when I objected to having to kiss all my parents' friends good night, and my mother sensibly agreed I could stop doing so, as long as I wished them good night politely.