That speed was achieved because the jet stream -- the air current that storms and jets travel along -- is raging right now, and was measured at 230 mph over Long Island on Monday. The LA Times pointed out that that was likely the fastest wind speed at that pressure level ever recorded in the US. So the pilots weren't even trying to speed: It was more like the plane was traveling at 600mph while the air it was traveling in was moving at 200mph.
The plane landed in London a full 48 minutes ahead of schedule. And it (kind of) surpassed the speed of sound (767mph), something commercial aircraft aren't even designed to do. But, because the air around the plane was actually what was moving so fast, the plane itself didn't technically break the sound barrier.
These high speeds in the jet stream are far most common in the winter, so maybe you'll have similar luck on your next flight.
h/t LA Times, Popular Mechanics