Yeah, they are. Pretty sure that all Mercury outboards less than 30hp are made by Tohatsu in Japan. I also had a "Nissan" outboard which was also just a Tohatsu.Not exactly. They were developed in partnership with Tohatsu, Mercury, and Nissan. They’re all the same, but not “re-branded” anything.
What is slightly misleading is saying that Mercury and Tohatsu have the "same" engine. They are the "same" because only one of them makes the engine, Tohatsu.