Mxsmanic writes:

I suspect that in this case the pilot may have been an unlicensed student
pilot (someone who had been taking instruction but had not obtained a student
pilot license yet), or his name in the database is different from the one
reported. There are quite a few pilots named Joe Stack.

Apparently inactive airmen certificates are also omitted from the database. So
he might have had a license, but it might have been inactive.