Correct, Fieldfare is a thrush, just English has some name like nick names or short cut in vernacular bird names.
Like in Spanish, Fieldfare is Zorzal real (Royal Thrush). I'm not sure of the etymology of Fieldfare, but like Redwing is kinda Red-winged Thrush in short
. So there is not "thrush" in its name but it is still a thrush.