CPU mining, there wasn't another way on those days. You'd do it solo and completely worthless (no exchanges, only dodgy use cases) but a good project at that time.
That is what happens when you are actually looking and testing new tech by yourself.
Discussion
So you were one of the dozen people mining bitcoin in 2009?
There were definitively more than that.
From my tiny country were about 15 people trying these things in the army. US and east Europe would be over a few hundred each, if not more.
This was well advertised on the public mailing lists, BBS and later on web forums.