There is no need to speculate. It's here at this link:
Of course, they are smart, they have to say he is not a leftist, for fear somone will pick this up.
Leftist Democrats ALWAYS run to the center as moderate after the primary to attract some conservative vorte & the moderate/independent votes.
So just becauise someone run to the center doeas not mean he is not at heart, a marxist or socialist.
Progressive is a code word for leftists socialists.