Great!
You still run 6.6.
If you really fallow the official instructions (OR mine) on how to install on linux,
go in the extracted folder SweetHome3D-7.2 and run the SweetHome3D file
(usually double-click on it and choose execute OR run as a program).
After launch check again the version.
You must have 7.2.
If that's true, update all settings related with SH3D (shortcut, file association, menu entry etc.)
To be sure, you could move (delete) the old folder (SweetHome3D-6.6) and you will see whats works and whats don't (shortcuts).