No, normal bolts. 100% not self tap.
The swing arm would be cleaned (after casting) and drilled, and tapped, by a computer arm. To me, it feels like the thread tap at the factory was forced-in just once... maybe. So, while it made a thread, it didn't remove the microscopic burrs from the threads. So, when the bolt was coming out, it bent the burrs the other way, and the burrs started to cut in into the bolt's threads, locking it in. I think, if a tap at the factory would be driven in a number of times, it would have flattened most burrs it created from the original thread cutting.
I have gotten a die/tap set and run the proper size tap like 4 times, the bolts would go in and out so much easier.
However, the bolt that snapped, it broke on coming out. Maybe I should have done a few turns in-and-out to preemptively polish somewhat the thread the bolt was in. Yet, I mean, it is a $25K+ bike. You'd expect such a bad thread quality on a Chinese one, but not on such an expensive bike. Bad threads just seems amateurish. In our day and age, this should not be an issue.
And it is NOT the only bad threaded hole on the swing arm. They are ALL bad. Some are just better than others. And some jam the bolt during unscrewing. It is a huge let down.
One thing I appreciate is that Triumph included the bolts that have a rather BIG allen key size on the bolt's head. So, you can apply a good torque without stripping the bolt's head (even more, you can break the d-a-m-n bolt by its stem!). The new hugger manufacturer, however, did not do it, its bolts are like 2 sizes smaller for the allen key, and, boy, do they strip easy. Not the thread but the hat where the key goes. Totally useless. I am so happy it stripped at the point where the extraction of such a bolt was easy enough with pliers. This made me realize I need a tap and better bolts, and a few drinks.