The pilot of the amphibious firefighting airplane departed from a land-based airport with a hard surface runway. The pilot reported that he was distracted during the initial climb by another airplane flying towards him on what looked like a low approach. According to the pilot, this disrupted his callout flow, and he did not retract the landing gear. The flight was part of a training event, and the pilot was supposed to scoop water at a lake northwest of the scene of a mock fire. When he arrived at the intended lake, another firefighting airplane had just scooped water and advised him to use a south to north scoop line. The pilot stated that he did his pre-scoop checklist, putting his hand on the landing gear lever and verbalizing “handle forward, four blue for the water,” as he was watching the other airplane. He said it did not register that the landing gear lever was aft and not forward or that there were four green lights instead of four blue. When the airplane landed, it decelerated quickly and nosed over before settling upright, which resulted in substantial damage to the wings. The pilot egressed the airplane without incident and saw the floats had separated from the airplane and that the landing gear were extended. The pilot reported that there were no preaccident mechanical failures or malfunctions of the airplane that would have precluded normal operation.