Since MJ is off riding his new bike, I'm going to say what I think def.
He hand tapped that hole using a pin in the chuck to center the tap using the dimple in the top of the tap.
A little down force is all that is needed to get it started straight.
Once you get it started straight, it tends to stay that way. I'd be careful almost all the way through on this job.
I usually chuck the tap and power it in part way, then stop and go manual after that because I don't have a tapping head yet.
I've tapped a pile of holes this way but never anything that big in that critical an application.
Although, with all due respect, he had nothing to lose at that point.
I bet the case would machine like butter, however, I don't know how it would be after he welded it.
I'd also like to know.
So far, everything that has surprised me has been completely unexpected.