The modern explanation to modern hams is that an antenna tuner is there
to keep the rig "happy". Modern folk are very busy people, they just
don't have time for understanding, but personification of these
inanimate things is apparently appealing.

Your anecodote demonstrates though how inadequate that explanation is,
whether happy rig or happy ATU.

I understand your feeling that your pride has taken a bit of a dent.
Well, part of the territory when predicting antennas eh!

The whole idea was to get the Kid on the air, and excited about Ham
Radio, by making his first HF QSO with his Dad.

I think the learning will come later-he is a Patent Attorney-EE and
Law degree. He impressed me Field Day when we were on an Island on a
lake in South Carolina on 900 watt generator power. Had a lot of
Impulse noise on RX even tho we were miles from power lines. Decided
it was from the SMPS powering the Computer we were using for logging.
The batteries on the Computer were good for ~1 hour, so we could not
disconnect the SMPS for long.

While we were fretting over what to do, he butchered up a spent beer
can, and enclosed the SMPS, dropped the noise considerably, I was
impressed.

I hope he enjoys Ham Radio, in spite of my questionable advice.

Gary N4AST