The entire family trotting around in Halloween costumes for 4 days before "business" wasn't leisure?
I mean he tried to present it as leisure.
Now, I have nothing wrong with the PM deciding hey, I have to go on a business trip anyway, so why not make it a leisure trip at the same time. Makes sense. But as far as I can tell, that's not how he presented it. He presented it as primarily a business trip with leisure being just an added bonus. Based on that, he was quite misleading since that was clearly a leisure trip first and foremost and a business trip a distant second to that. Had he been honest about it and paid out pocket (minus legitimate security), fine. But that does not appear to be what he did.
If he's going to portray it as primarily a business trip, then we have every right to question why he didn't just use Skype.