GA Maintenance Technician reported learning that a C140 aileron was installed incorrectly during restoration of aircraft leading to an off airport landing.

Narrative

On Day 0 I was sent pictures of Cessna 140 that showed that the left aileron was hanging loose with only the inboard hinge holding it onto the wing It had made an off-airport landing because of it. I was informed that it was on a ferry flight from ZZZ1 to ZZZ2 to have the Annual inspection performed. I was also informed that he thought the airplane was out of annual and that I had done the last Annual on it. I had done an Annual on it 20XX. I had done a ground up restoration in the aircraft over the course of about 3 and 1/2 years. Over the last 4 days I have thought about what may have occurred. The restoration had been performed at my house which is about X miles from the airport with the majority of my hardware at the house. Assembly of the aircraft with the wing installation along with the flight controls was at the hanger located at ZZZ. I had not intended to install the ailerons that day but a friend showed up at the hanger and volunteered to help. Since most of my new hardware was at the house; I found hardware at the hanger that I could use on a temporary basis just to get them hung with the intention of replacing it with the correct items later. In the course of events with rigging of the flaps and ailerons and going out on a 17-day trip with my primary work as a pilot; it was probably 3 weeks before I installed the cover panels on the ailerons. Since I do not normally make temporary installations of hardware in this manner; I forgot all about replacing it with the correct items. I try to make a habit of checking inside of any inspection holes before installing panels but why I did not this time I do not know.In the future I have every intention of double checking my work; and inspection more closely before closing up panels. One look at the airplane will tell you that this is not normal for me and I will not let it happen again.