Aircraft Technician reported not pulling the Landing Gear Downlock Pin during pre-departure inspection; which resulted in a gear disagree and air turnback.

Narrative

Aircraft had an air return for a gear disagree. Upon aircraft landing an inspection was conducted and the gear pin was found still installed and the tow pin was discovered in the gear pin holder in the flight deck. As aircraft returned to gate after an air return due to a gear disagree EICAS message; it was discovered that the aircraft tow pin had been pulled and stowed instead of the Nose Landing Gear (NLG) downlock pin. I myself was a part of the pulling and stowing process. As I was leaving the flight deck I verified that there were indeed 5 pins put and stowed away in the box before signing off gear pins in the logbook; not realizing the NLG downlock was still installed due to the wind blowing the flag of the downlock pin up and around the NLG. After the discovery; the NLG pin was pulled and stowed in its correct location fixing the air disagree EICAS issue. It was noted from the flight crew as well that they did not see the downlock pin still installed during their walk around and noted seeing 5 pins stowed in the flight deck before departure.