Beer already at FG?

My kit is Brewer's Best American Light. I used bottled spring water and followed the instructions exactly and it has been in the primary for seven days. OG was 1.041 exactly what the kit said it should be. The instructions suggest a final gravity of 1.010. I just finished racking it to a secondary, I took a gravity reading and it is already at the suggested FG. It has only been seven days! How is this possible? The kit says to let it go three weeks for total fermentation. I tasted it and it already had a twinge of carbonation. It tasted pretty good but almost cidery. There were bubbles rising in the graduated cylinder. Is this normal?

Definitely normal...

Fermentation produces alcohol and CO2, so even at this early point, a small amount of that CO2 is likely to already be disolved in your beer. And yes, for a beer of that gravity, it's definitely not unheard of for the very first stage of fermentation to be complete after 7 days.

However, a caution: just because the yeast has finished converting most or all of the sugar it's going to convert, that doesn't mean the yeast is finished with all its work. You definitely want to give it another week or two (more if you're patient!) to let the yeast finish cleaning up any byproducts (like that cidery flavor you're picking up!).