I must admit I'm a bit shocked at how many posters are being extremely judgemental about the grandparents, when we don't know how long they actually stayed over, or how much time they normally spend with the GC's. The OP says herself that the kids were 'really badly behaved the whole time', so if she felt that, when she's used to being with them, it's hardly surprising the GP's found it too much. Also, maybe what they said was intended as a bit of a joke, but perhaps the OP didn't take it that way, because she too was feeling frazzled after all that had gone on.
So my questions OP, are, how often do the GP's see your little ones on a normal basis, and how long were they with you over Christmas? Also, are your kids normally well behaved for their age, or do you normally find them a bit of a handful?
If the GP's only normally see the kids for a couple of hours, once a month, but then stayed for 3 days over Christmas, then I can totally understand why they said what they did. OK it wasn't worded well, but then we all say things badly at times. On the other hand, if they see them twice a week for a whole day, and only spent 24 hours over Christmas, then yes, I would say they reacted badly.
Personally, I think this is something you actually need to have a chat with them about OP. Perhaps give them a call and ask them if they really meant what they said about only seeing the kids on video for the foreseeable, then see what they say. If they say yes, then perhaps point out that this will mean that they are likely to lose any closeness that they do have with the children, as little ones, really don't understand the concept of video, and won't want to sit still just to try and speak to Grandma/Grandpa. Then maybe acknowledge that the kids really weren't at their best over Christmas with all the excitement, and suggest that perhaps future visits are limited to an hour or two until the kids are a bit older, and less likely to get over excited. However, like I said earlier, it's really hard to judge this until we know the answers to my questions.