I will tell you my experience this past summer.
I went to Australia to see my parents with my 16 year old DS. DS has autism, adhd and had just finished his GCSEs. So he was quite unregulated. And he needed alot of down time in order to get himself back into being a human.
I was scheduled to see one friend of mine - I was travelling an hour to see her and she was travelling an hour to see me, we met in the middle.
My parents do a good line of lamenting that they live so far away from us, and have not been able to see my DS grow up. Both were also teachers, so not unused to kids. My mother in particular likes to weep and wail and get consoled by her friends about the fact she's missing out on so much.
I asked my parents if DS could stay with them while I went to see my friend. All he would have done is stay in his room, or on the sofa with my mother and watch films. He's not violent, he's not rude, but he was very tired and so was very quiet.
They flat out refused. They said that they have done their parenting and were not going to be responsible for another person's child- i.e. their own grandson who they trumpet to all and sundry how much they miss. So I told my friend I had to take him with me. She was very understanding. Did it change the dynamic? Yes, it was pretty restrained. Thankfully we were in a city so he could go and wander a bit by himself, but the wretched child forgot to take his own phone so that was a bit fraught as well as I was worried about him.
I was desperately hurt tbh that my parents couldn't just step up to the plate. I can hand on heart say I have never asked them to look after DS at any stage- they barely see him. He was not a baby. He would have just sat around and been quiet, patted their cats, taken their dog for a walk at best.
So just saying that not all grandparents seem desperate to spend 1-1 time with their kids. Not all even welcome them that much. Your friend may have that sort of situation going on.