Probably a security thing.
Early german tanks were called "tractor" to hide the real purpose.
Early designs of US tanks (M1's and 2's almost look like M3 Stuarts) were called "combat cars" too.
US also had nomenclature that was at best confusing. For example M3 Stuart light tank, M3 Lee medium , M3 halftrack.
I read somewhere that they did that on purpose.