Usually it’s spoke tension but it can also be:
Improperly heat treated aluminum
Inclusion or other artefact in the extrusion
Are common issues with some manufacturers and exhibit themselves as damage in that manner. I had a velocity rim that did that at 60 kgf and on the other side a Stans rim at 100 kgf. Both were wheelsets I built and serviced regularly.
The wheelset is not necessarily done right away. The Stans rim mentioned above went 7000 miles with similar damage that did not get worse and the wheel remained true.