The thing I hate about this statement is it gives people an excuse to ignore things they don't understand at first glace by claiming the presenter doesn't fully understand it so it's probably not true.

Its a good standard to hold yourself to when explaining things to others. But not one to hold others to when explaining to you.

OTOH...

"Hell, if I could explain it to the average person, it wouldn't have been worth the Nobel prize." -- Richard Feynman

I agree with your statement, but we're discussing physics reporting in the news. They are aiming for eyeballs and ad clicks, not for emanating understanding of the topic.

If you can successfully eli5, that indicates thorough mastery of a subject. Stuff on the bleeding edge of physics can be grasped by a limited group of experts, but nobody might have developed the 10th dan sensei level understanding yet. Maybe in 50 years we'll have great explanations of black holes and quantum mech that laypeople can grok.