Bobby Knight is just being crafty with his words here. By not defining himself as a partisan Republican, he is opening the door for lots of Democrats to cross over and vote for Trump. Those Democrats won't feel like they are being traitorous to their party because while Trump is running as a Republican, the establishment Republicans hate him and so these Democrats will feel like they are giving the Republican party a poke in the eye by voting Trump. And they aren't too crazy about the choices on their side of the fence.
Trump is now in general election mode. Going to need a lot of cross-over vote to win in November. So I expect a lot more of this type of campaigning.