"Close" is a relative term. And since he didn't mention a specific distance, there is no way to know how close to him was "close". Without knowing at least an approximate distance, we have to eliminate human error first, before going to the time and expense of replacing costly electronic parts that may or may not be defective. But presuming that he fully charged the battery before flight, we still need to eliminate the possibility that he simply flew it beyond the effective control range, and it simply dropped after the battery could no longer power the motors before he could have/would have moved closer himself, to regain control.