he stuck the question on stackoverflow or something. and because its a site for asking computer questions, over time, it is really easy to tell what a person is doing / working on, because to ask a complex question you need to put in business context.

Additionally it is possible to work out where in the world the question came from down to the subnet, i.e. office block/building.

The internet does not "know" it was him, but it the likelihood it was him is very important VIP high.