No, that's confirmed nothing for the main pairing. If anything, that's just kill the poly ending. I don't see the point if the main pairing ending is just a copy of a side couple. The main pairing ending should not be the same as any side couple we have seen because it would feel like they just copy the dynamics of them rather than having their own, plus just because a poly work for someone doesn't it will work for anyone. And also, it will feel forced to me, i mean a kiss between the other part of the triangles who for no reason start to fall in love for each other over a simple kiss (doesn't make any sense unless they had feelings before) and now by pure chance, the MC stumble on probably the only poly couple of the town which happen to be 2 of their senseis, i mean that she would have found that her senseis was going out together would have been a matter of a time but she may not have known it was poly.
You know, i rather have an ending with the childhood friend and the friend going out together. Now that's would be original.