You've started a 2nd thread by accident perhaps?
This does sound a bit ott, but they will be exhausted and stressed out of their minds. Not to mention dil will have huge amounts of hormones etc telling her to keep anything that feels remotely threating away. If you have not had a close relationship previously or have been perceived as unsupportive/judgmental/dismissive/demanding/anything like that, she might be feeling a very powerful instinct to keep you at arms length. Your son might be trying to head off a diplomatic incident while hormones are high and sleep quality is low, knowing that in a couple weeks everyone will be feeling more like themselves again? My advice would be to just trust him and go with it. Be helpful and supportive, offer to make your own cups of tea when you're there, prioritise mum and baby - it's their time right now.
Please do not fall into the trap of 'I have never been/felt/acted like any of the above so therefore I will stubbornly bulldoze on through whatever this is'. Sometimes people percieve things differently to how you've meant them. That doesn't take them horrible people, just mistaken. The thing is you won't change that perception by getting in a snit about it, the better way to correct this is to demonstrate the sort of person you actually are in your actions. So demonstrate your respect for the new parents, help them etc.
I hope you and your grandchild have a lovely bond, in good time.