Nooooooo chance. 0.0% chance Kawhi Leonard said this. The man who doesn't talk any shit and lets his game do the talking is going to say "someone tell LeBron to stop being scared to guard me?" Yeah OK pal. It's the Stephen A method to a tee. A "very reliable source" my ass. What about all those reliable sources that said he was going to sign with the Lakers? This sounds more like something Patrick Beverley would say, not Kawhi who maybe utters 10 words all season. He's going to waste that on talking shit about LeBron? Again, no chance. Just think about this rationally. Why the hell would Kawhi say something like that? What purpose does it serve? Not to mention he has his own issues with load management and all that crap. Everything we've seen and heard from Kawhi over the last few years suggests that this would be the last thing he would ever do. While I appreciate the attempt to make a LeBron/Kawhi feud happen, you're going to have to do better than this.
If I had to guess, the source was Uncle Dennis and it was something that HE said, not Kawhi. That feels way more believable. The best part about this whole thing is if you look at the games these two have played against one another, you could argue Kawhi was dodging LeBron. In their first meeting Kawhi only guarded LeBron on 8 possessions. Both Maurice Harkless and Patrick Beverley spent more time on him. Now things did get better in the second matchup on Christmas, with Kawhi guarding LeBron on 16 possessions, but then LeBron matched up on Kawhi a total of 12 possessions which was the 2nd most on the team behind AD. So as you can see, the evidence doesn't really support Stephen A's claim that this is something Kawhi actually said.
Also, pretty hilarious caption in that video about being concerned about the Lakers. Concerned about a team that's 30-7? A team that has a top offense/defense/net rating/point differential? What a weird thing to say.