You can't rely on the oil light to tell you when the oil level is low, that's not what it's for. It's a pressure indicator and will only come on when the pressure drops to almost nothing, around 2-3 psi. If it flashed for a second as you came to a stop, it may have been because the level was low enough that the oil in the pan sloshed forward and the pickup momentarily sucked some air.
Check the oil level again with the engine cold, and add more slowly until the dipstick reads in the normal range. Don't be afraid of adding too much, just don't dump in the whole quart at once and keep checking the dipstick until the level looks ok. A slight overfill is preferable to leaving it underfilled.
Although there is really no way to determine the long-term effects, your engine is probably ok as long as you didn't run the oil fully dry which it doesn't sound like you did.
More important is why the level was low in the first place- How long ago was the oil changed and by whom, and have you been checking the level regularly (or at all)? You need to be sure there are no leaks or internal engine problems causing abnormal consumption. Best thing to do is change the oil, making sure the proper amount is used and the dipstick reads full, and then check the level at least once a week to see if it drops. If it does look for leaks, if there are none it's time to check engine internals.
Of course since the car is new and under warranty you can just have the dealer do all this.