Doesn't matter, because he isn't the SoS. And the meeting happened over Easter weekend, when Rexxy was still on the job (his last day, I think). Any way you slice it, this maneuver is super sketchy. You definitely don't send an unvetted guy to do the job that he hasn't yet been approved by Congress to do--much less a historical meeting like this one.
Expect this to toss a grenade on his confirmation hearings. Congress critters don't like being overstepped like this, especially when they still maintain power over this guy and Trump in this matter, and especially as the repubs that might have a chance of supporting him are currently scampering away from this sinking ship that is the Trump GOP. A lot of these people actually still care about precedent and procedure, and certainly the power and duties assigned to them.
This maneuver is nothing more than a big fat "Fuck you all and fuck your laws, I'm Trump and I don't care about you so fuck you!" from King Cheetoh. Even if one of these guys supports him in general, this isn't tolerable from their perspective.