I guess it can be because of the Windows 8.1 OS yes. So I tried the following:
1- I exported this game (lets call it game1) for Windows 8.1 Universal in Construct2 r212, and then I opened it with my VS Community 2013: Then the package.appxmanifest wont open and in this case it gives me an error that says : "Unable to load manifest designer"
2- So I tried downgrading Construct 2 to an older version (r206): I couldn't open my game1 in this older version because it was created with a newer version of Construct2.
3-Then I tried an older game I have=game2, exporting it with Construct2 r206 for Windows 8.1, I opened it with the same VS Community 2013, and the package.appxmanifest opens perfectly well.
4- I upgraded my Construct2 again, to version 212.2, then I again exported old game2, and again in this case the package.appxmanifest opens without problems.
So (correct me if I'm wrong) it seems to be that for whatever reason there is an incompatibility between games created with Construct r212 and both VS 2013 and VS 2015