Eeeeehhh... Not so much a holiday, really. We had a seasonal cycle in the old dome, so it tended to be in the colder periods... almost wintery? And so I guess you could say that meant it happened around Christmas or some other winter type holiday. Mistletoe itself tends to be a Christmas thing.
But, with no seasons here, I'm not sure what they're going for. The only thing I can think of is that they thought it was a holiday because it happened a couple times there. But, I wouldn't say the bots themselves were a holiday event specifically. At least, they were never announced as one.