Brisket Help

I cooked a 6.5 pound brisket yesterday and have a question. I planned for the cook to take approximately 1 hour and fifteen minutes to 1 hour and 30 minutes to cook to an internal temp of 190 degrees. Much to my surprise, it only took a little over 4 hours. I cooked at a dome temp between 230 and 245 degrees. The meat was probed to monitor the meat temp throughout the cook. Once I reached 190 degrees, I checked in several places with a Thermopen to verify. Also, the meat remained in the plateau for less than 30 minutes. Finished product was really good but I am confused as to the previously described. Anyone have an idea why this happened?