In legal terms, this might well meet the definition of premeditation, as the article said. Grabbing a murder weapon, carrying it with you to meet your victim, and driving them to another location to carry out the murder probably more than meets the definition. He was clearly sloppy, and it certainly seems possible that he was wishy-washy to an extent (possibly hoping to talk things out with Lee somehow) but I don't think those things matter too much legally.
I am, if it's not blindingly clear, not a lawyer.
A killing is never really "rational" from an ethical or moral standpoint, except for extraordinary situations like self-defense.
But premeditated murders are rational in another, more purely functional sense of the word: the killer was not untethered from reality, they understood the consequences of their actions, and took a series of concrete steps toward achieving the murder.
Combined with the stabbing being with a kitchen knife, I’m inclined to say he probably wasn’t entirely rational at the time, and more of a spur of the moment thing.