Everyone's a GM on sundays.
After playing in 3 or 4 15/10 tournaments this sunday, I've watched more than 5 games which resulted in a ~1210 player beating or drawing 1500-1800 players. I've seen a player who has hardy ever lost a match, has a winning streak of 58 an a losing streak of 1. I've seen a player who moved every 10 seconds; I could set my watch to it. I've seen ~1400 player beating me in a draw, after each game under analysis, they never made a wrong move.
A majority of these players have had their accounts for a while, though none of them were premium members.
This might be an anomaly, a freak occurance of a hoard of players playing at much higher levels than what is displayed. A bevvy of sudden grand masters whom lay waste to an entire tournament with great ease.
Hold on to your pants, world! Sunday morning is not only the day of the lord, it's the day of the level 1300 grand masters!