How is this kind of soldering done?
I suspect it has to do with the pad geometry.  The pad rings look very narrow with a fairly large hole (for the pin size) which prevents the normal solder fillet from forming.  Notice there is more of a fillet on the larger square pad for pin 1.  There are robots that do the soldering ensuring a measured amount of solder on each joint.

It does not look like paste in pad (using the stencil process to put paste on the through hole pads), as you would end up with paste on the pins if they were inserted after paste was applied.

It was probably not done on a selective solder machine (like a one pin wave soldering fountain) because there is no access on the bottom side and the pins on the top would end up with solder on them if selective soldering was done upside down.