Extremely Quick Fermentation ?'s

I brewed a India Brown Ale Wednesday night (7/23) and pitched my yeast around 10 pm. The OG for the recipe was 1.070 mine ended up at 1.074.It took off rather quickly and was fermenting pretty good and was still going strong on Friday the 25th. Today (Saturday the 26th) at 1 pm I have no airlock activity at all. I take a hydrometer sample and my gravity is 1.018, the recipe says the FG is supposed to be 1.016. Granted I pitched a nice starter (1968 ESB) but that is still quick as hell. The beer actually tasted good as well. Why the quicky?

You must have done everything right. Good job. Give it some time and it will probably come down to 1.016.

Fermentation can take less than 24 hours, three days is normal.

Just leave it be as long as you can resist before the next step.
I'd give it at least another 2 - 3 days before doing anything.

Ive had many a beer take off early. Give it time to mellow out. Should come down to FG after a bit.

then let it sit for the yeast to finish. it will help clear the beer, I usually go three weeks before even taking a hydro.