That's true for small planets from Murcury up to about 2 times earth masses. With some notable exceptions such as IO thats Tectonicly active due to Gravitational Stresses.

From about about 2 to 3.5 Earth masses it's guessed you only need a large moon, or oceans, but not both to be Tectonicly active. Earth needs both.

And from about 3.5 to 8 Earth mass neither a moon nor oceans are needed for a techtonicly active planet.

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