Christmas is high risk for all the domestic pets really.
People who are unfamiliar with animals, or strangers to this particular animal, who may over-step the boundaries and not read body language correctly.
Animals can be easily overwhelmed by one or two strangers, so a whole houseful of strangers is a recipe for some sort of drama.
Drinking - lowers human inhibitions, which can really alter body language and behaviour, further exacerbating the above two problems, really freaking out dogs and cats.
Theres more food unattended: chocolates, mince pies, christmas cakes, yule logs, cooked bones, alcohol (particularly creamy stuff like Baileys, Advocaat), hot chocolate with alcohol in it... all of this can kill a dog or cat easily, particularly if no one notices due to being busy, tired, drunk etc, that they've eaten it or that they're showing signs of illness. Or of course, they don't know the animal well and so don't recognise signs of illness.
Add in that the dog in this scenario is young, in a home they're not familiar with, with NO familiar, safe, reliable person they have a history of responding to, being rewarded by, their owner is away which also increases the chances of a problem.
This could, even if no one gets bitten and no one eats something they shouldn't, be a horribly stressful and uncomfortable time for this dog. The chances of things being fun, relaxing and happy for them are extremely low!