I amused myself (and katkt too) for the rest of the evening speculating about what exactly that means. Hard like a truck? Fast like a truck? Does he only do it on the open road? Does he squish people? Is he LOUD?
Well, when I saw the instructor again today (T) I decided to mention this and how funny it was. Apparently she hadn't noticed the lyric and said she would look it up. Ten minutes later I saw her making an air-horn motion and giggling to herself.