[TheEzEzz]

FTA:

"These associations remained significant even once the researchers controlled for political party."

This seems to rule out the correlation coming from manual labor being associated with conservatism.

[randomknowledge]

The headline was "Men's Biceps Predict Their Political Ideologies" you can't rule out political idealogical in a study about political Ideology. There is a spectrum of belief within political parties which explains why the association remained.