He was still high on a historic title, especially after realizing what a special teammate he had in Kyrie. He, like everybody else, probably FIGURED that the Warriors with Durant would be a tall task, but didn't KNOW it, yet.
If LeBron had wanted to go to to the Lakers then there obviously would have been conversations occurring behind-the-scenes and they wouldn't have signed Deng and Mozgov. Even if LeBron had made it known that he'd keep an eye to the future with the Lakers in mind, they wouldn't have signed them.
I truly don't believe LeBron started seriously considering the Lakers until we lost Kyrie. The '17 loss stung, but I think he was confident enough in Kyrie and supporting cast that he didn't feel they couldn't return and gave it another go with a few adjustments (which should have occurred after '16, only we got fat and happy and made a ton of wrong moves.) He even famously told Kyrie "we'll be back" following the '17 loss...I don't think he would have uttered those words if his mind was preoccupied with LA.
Griffin saying that LeBron was gone after the '16 title is just him trying to compensate for the lousy job he did that summer. We didn't sign a backup PG and thought broken-ass Dunleavy (later, Korver) was the answer to GS adding a top-2 player in the league. Truthfully, there is no legit counter to that but adding a couple defensive-minded players a la Houston while you still had the '16 title core in place was the way to go about it. Griff horribly bungled it.