As a kid returning from California after a 3000 mile trip and having learned just how bad Massachusetts drivers were by comparison with my experiece driving cross country and back, I got on the Massachusetts Turnpike and was immediately passed by some fool going over 100 mph and he was closely followed by another car at the same speed. Knowing my Massachusetts drivers, what was happening was the second car was playing cop by chasing the other guy because he was going to fast. Happened all the time back then. I had traveled perhaps 7000 miles all over the country without any of the type of driving that was common in Massachusetts only to immediately encounter it as soon as I got back.
Sounds like Massachusetts.
The traffic around Boston is brutal and the drivers are the worst in the world! Just in the past week I had to lay on my horn at the car behind me in two separate occasions as they were getting ready to pass me on the left just as the lane was merging ahead. If you are going at any speed resembling the speed limit drivers behind you get very bent out of shape. Massholes!
As someone who learned to drive in Boston, I think you may have misinterpreted the situation. I never encountered anyone "playing cop". The second driver was more likely following closely and perhaps blinking his lights at the first driver in order to get him to move to the right lane so he could be passed. There is no speed that is "fast enough" on I-90 (or the Autobahn). If you aren't in the process of overtaking another driver, you should be in the right-most lane.