My guess is someone’s car must have been broken down on the side of the road. They would have ran over to the phone booth to call for the tow truck driver to come help them out. After repairing the person’s car, they would have left, just as Michael drove by to see the tow truck driver. Michael would then pull over and kill the driver, and steal his coveralls and boots. How the Rabbit in red match box got out of the car is anyone’s guess.
I assume it’s possible Michael could have seen it and thought, “I don’t need this”, and tossed it out. Either all that happened, or Michael was driving beside the tow truck, and rammed it off the road to that area. Another possibility is the tow truck itself was broken down on the side of the road. Really though, it’s not that important, and isn’t meant to be known. The aftermath that Dr. Loomis finds is what makes it creepy.
I like that he never speaks. He’s capable but chooses not to. Adds to the creepiness of the character. I think it would ruin the mystique of Myers if he spoke.
In the 2018 movie, Sartain says that Michael can speak, but chooses not to. It’s possible that a biopsy was performed on Michael’s larynx and nothing was found to be physically malformed with his ability to speak. Indeed, in the first movie, we hear him grunting another of times. He definitely CAN speak, but for some reason does not.