He probably filled it to the upper hash mark on the dipstick. On most cars, the volumetric difference between the upper and lower hash marks is about 1 quart or 1 liter.
I like to keep mine in the center, that way I can see if the level goes in either direction. I just recently changed my oil for the third time, and I find each time that 3.5 quarts (as eyeballed on the jug's molded-in graduations) is pretty much dead center on the silly orange plastic indicator as seen the morning after the change. It can be difficult to see with fresh oil- I often have to wipe it several times and have the lighting
just so.
I like that you can see and even reach the filter from the top of the engine. Makes it easy to do a quick check for tiny leaks, or in your case, that it's suddenly a different color.