You want to argue that trump literally had an R next to his name on the ballot. Yes everyone agrees with you. He literally had an R next to his name.
What Darth is saying is his stance on issues came nowhere near Republican orthodoxy. So much so that he is effectively third party and draws votes from different sources.
I did an article on this already so I wont go into more detail but I encourage you to look at a county by county breakdown of PA for the toomey senate race and trump presidential race. You will see that they get their votes in different places. Trump is literally and figuratively bringing a new wing into the GOP. A wing that was previously in the middle, and some even democrat. It is up to the GOP to rationalize the conservative wing and the nationalist wing to make sure each side gets what they want.