That is just not true mate. A better working definition for temperature is the average kinetic energy of molecules not average speed of them. Smaller molecules such as hydrogen will move much faster than larger ones such as water at any given temperature. KE = 1/2mv^2

And no a thermometer in a vacuum will settle to the ambient temperature of it's environment. Nothing will settle to absolute zero. Either an object is in a true vacuum (theoretical doesn't actually exist) in which case it will remain its current temperature forever or for objects in the vacuum of space it will equalise with the temperature of it's surrounding environment.