The IRB regulation says that a player is eligible to play for a given country if he has three years uninterrupted residence in that country and hasn't yet been capped by another nation. It can get even weirder -- Sonny Bill Williams (for example) was briefly eligible for France before he chose to return to New Zealand and be capped as an All-Black. Manu Tuilangi has lived in England since he was relatively young -- he has older several brothers who played (or still play) for English professional sides. His family saw that as an opportunity for him to get a good education and they took it. He played U14 and U16 rugby for his English high school and therefore qualified for England under the three-year rule. Ricki Flutey managed to get capped by England under the same rule, even though he was born and bred a Kiwi. And of course the AllBlacks generally have at least a few players on their side who were born on one of the Pacific Island nations but immigrated to New Zealand to pursue an education there.
Sekope Kepu was born in Oz swoope. His family moved to NZ when he was a kid. edit: As for Cooper Vuna, yes he was born in NZ. Ufortunately he didn't stay there
BLM nailed it. I was keen to see Tuilagi play for the Manu Samoa along with his other brothers but he has done what is best for his career so kudos to him. As BLM pointed out there are regulations so you've got people like Sekopu Kepu, Thomas Waldrom and Cooper Vuna among others who were born in one country but play for another
