i believe he get for each games some points , for the ASD voting and the position who he achieved most points is the selected one. Last season i would have said it is the position where he playes most, but this season my PG/SG backup got elected as third SF in the Voting and i am pretty sure that he plays less there then on the guard spots(at least games, probadly also minutes).
Your big SG played the most time on a Guard spot, and he makes better games rating wise so i didn't wonder that the fans still see him as a guards, even if you played him the last games on the C spot. Nice trainee by the way, i like those guys who are big and starting with good guardskills(and the other way round).
I think the record just count through the number of visiotrs through that voting, and then also the stats get considered.