That sounds unethical.
Edited to add, not what you were doing but what he was doing.
Yeah I would say it was definitely sketchy ethically. I happened to pick up on it because I subscribed to the website and noticed it happen a couple of times in a week before I started actively watching for it. I’m sure I wasn’t the only one who noticed - when I did do those trades, you could see other people playing it the same way.