Good question.
I just looked this up and it's actually a Loyalist Bar in Benidorm (next door to the NI Supporters Club bar). So I assume that the Norwegian flag is there a) To entice unsuspecting Norwegian tourists in to partake of "Are Kulcha" and b) because it is red, white and blue?
Here's the classy hordes celebrating "The Twalf" outside the same bar - including them singing (32 mins) "The famines over, why don't you go home"... to Irsh Catholics... whilst in a foreign (mostly Catholic) country. God Bless King Billy!
I wonder how many Norwegians tourists are in Benidorm waiting to be enticed. (As a Scottish person, have to say the Saltire wouldn't entice me in but guess I've more experience of this kind of thing than random Norwegians.)