Cal Thomas as Statist

That's not the first thing he struck me as, that's for sure. Isn't that sort of a stretch?

Not at all, your definition says:

...a system that involves a significant interventionist role for the state in economic or social affairs.

In common usage during political discourse, the term has evolved in an American context to refer to those who advocate for centralized control by the national government. The next, closest term I could have used was anti-federalist, but that term has become somewhat anachronistic, even though it is still accurate.

Cal has repeatedly written, directly and indirectly, that he believes regulation of most every social and economic aspect of American life is a proper role for the national government. That's why I would have previously said (and did say) that Cal is not really a conservative. In truth, if we consider F.A. Hayek's argument, Cal is a conservative since central control, authoritarianism, and socialism are all aspects of American polity that are advocated by "conservatives" today.