I was curious if it's seam welded tubing, but too lazy to check. There are lots of good tubes that are seam welded and then drawn. Some of the high-end stainless, for example. Some tubes occasionally make it through with defects. The late, lamented True Temper tubing had a lot of such failures in the early days.

Vintage Reynolds 531 sometimes made it out of the factory with grooves cut on the inside that would fail like this. That tubing was pierced and drawn, no welding.