I've had similar situations. If you are in a public space, other runners are welcome to do what they want, as long as they do not interfere with you or physically contact you.
I remember a similar situation at Ohori Park in Fukuoka in 2002 when I lived there for a while. I was doing a moderate pace run, but I felt very good. I saw a very good runner doing a fast paced run, so I decided to speed up and "draft" off him. He had a coach alongside on a bicycle. I sped up to his pace (about 3:00/km) and stayed about 8 feet behind him. I wanted to draft off him, but I didn't want to distract him at all. The coach looked back at me and tried to wave me off and "shoo" me away. I yelled "Hey man, this is a public park!!! I don't speak much Japanese, but I think that he got my drift.
He continued to try to shoo me away. I just threw in a fast 200 and smiled as I went past.