Oops, you're right, it's the other way round; UK nationals in the EU can vote in Parliamentary elections but not the referendum.

The great thing about democracy is there are so many different electorates to choose from.

As far as I understand it, the eligibility rules for the EU referendum were exactly the same as for Parliamentary elections: UK nationals in the EU were only eligible to vote if they'd been abroad for less than 15 years.

The Scottish independence referendum was the oddball one, largely at the request of the Scottish government from what I can tell. It required actual residence in Scotland but little else.