Because the political spectrum in this country has moved so far to the left, Norman Thomas would be considered moderate or even slightly conservative today, at least on matters other than economics and foreign policy. As far as I know, he did not favor the cultural radicalism that has been a hallmark of the Democrats since the rise of George McGovern and has made inroads into the GOP.
I have read that conservative theorist Russell Kirk voted for Norman Thomas because of his opposition to intervention abroad.