How do you know he was trying to catch you? Sportbikes are extremely fast on the highway. AT THE TRACK, I ran a 7.1@102 in the 1/8th mile on my 03 Gixxer 750. Years before that when I was 19, I tried racing a sportbike in my 2001 Miata on the highway. Boy was that "race" an embarrassment.
Food for thought as well: Sometimes I would follow drivers fairly closely in order to avoid the buffeting wind from knocking me around. Maybe he was just doing that, but once you started going a little too fast, he felt like not following anymore, or just thought he was making you uncomfortable and that's why you tried to put distance between you two.