OK, given the mileage and the photo It's fairly safe to rule out brake track wear. However it's hard to tell from the photo, and a stone embedded in the brake shoe could have cut a groove, considerably weakening the rim. If there's an external groove at the crack that's the likely cause.

Otherwise, we now come to the issue of side stress caused by the tire, and my question about the tire width.

Since the hoop stress on the rim is based on width and pressure, 105 is meaningless with knowing the width. If this is a narrow rim, where the maker expected you to mount tires in the 25-28mm range (hypothetical example) and you mounted a 2" tire and took it up to 150, it's easy to see how the flange could be over stressed.

I gather you didn't buy from a dealer, so have no way go enlist his help on a possible warranty claim (no groove, narrow tire). You might ask someone with some expertise and credibility to look at it and offer an opinion, and use that to resolve with the maker.

Otherwise, you may have recourse through local small claims court.

But, before calling it a defect, you have to eliminate the two scenearios I described.