Did you return in July or August this year, never saw any flights so low returning in August. If you returned in July you can pick up flights a little lower.
If you booked a long way in advance you also might have picked up a lower price before the big hike but this summer most have had to pay £700+ for economy, £900+ for premium.
Always possible you picked up a price glitch either, it does happen I have had my fair share, 3 times in recent years.