maemo (Nokia) + moblin ("Intel's Linux") = Meego
Sailfish is based on Mer, which is a community project based on Meego, but Mer actually started already before Meego
And then there is Tizen, which is also based on Meego
"Jolla was created as Sailfish and escaped from the burning platforms of Nokia to develop the MeeGo (formerly Maemo) Linux OS for phones"
Jolla is the company, Sailfish is the OS.
"Nokia began work on what today is Sailfish in 2002" is as true as saying Linus started work on it.
Sailfish is based on Meego but differs quite a bit. And Meego differs a lot from Maemo.