I'm not criticizing, but didn't you notice him maintain a consistent distance from you?
I accidentally pulled in between a speeding motorist and an unmarked X5 on the motorway a few years ago. The motorist in front pulled away, I made progress myself, but noticed the BMW maintain distance behind me immediately. I pulled in to Lane 1, took my foot off the accelerator and slowed to just under 70. He pulled me, told me I'd got in the way of him catching the other chap and that I was to drive safe. He then wished me a good evening and left.
If I hadn't of noticed him when I did, I suspect my ass would have been grass