Angels often use non human messengers, you know
I'd say it was very likely a sign that everything was going to be OK for him and for you.
Birds have long been associated with the afterlife. The idea of them carrying the soul to heaven is particularly popular in many cultures, and they're often seen as the form of the soul, too.
I love birds and I keep three now. I watch them a lot. They have a wonderful instinct for bringing comfort. Birds are very sensitive creatures, and really very clever, even the very small ones. My favourite budgie always knows if I'm not well, and it's very sweet to see him watch me with concern.
They also know at first sight who is safe to sit on and who isn't, and mine will choose the most gentle person to be near. I think if a wild bird will land on your Grandad that's a huge compliment!