It may be worth glancing at this more detailed answer that discussed how aluminum rims were constructed. But in brief, aluminum rims are first extruded in a flat bar, then they’re cut and rolled into hoops, then the ends of each hoop are joined somehow.
One method is to simply pin the ends together without smoothing out the joint. Your rim was built this way, and you’re looking at the seam where the ends were joined. Basically, this is there by design. Look in the corresponding location on the other rim and you should also find a seam.
On higher end rims, the joint is usually welded together and the weld is sanded down. For practical purposes, I believe that the advantages are mainly cosmetic. On pinned rims like yours, you might sometimes feel a bit of a pulse when braking (assuming rim brakes, which you have) when the brake pads pass the seam.
If you hit an obstacle, a more common failure mode would be for the rim’s bead hooks to get dented or to buckle. If the rim cracked, I think it's not likely that it would crack in such a straight line.