Today I heard a hiker who was carrying his two meter radio on a local summit. He was taking a break and was making contacts. I made a contact with him and quizzed him about his location and radio equipment. He was on the peak and was using a battery powered handheld. He was familiar with SOTA but had not registered in the database.
As far as I can see, the general rules do not require that an activator be registered. As long as the activation was “conducted in the spirit of the programme”, it would be a valid activation and a valid chase.
From my experience I can say that this is quite usual. I am also not participating in SOTA but I am calling CQ from the summits from time to time. Chasers then ask for the name of the summit and log me.
As stated already it is valid. Like every QSO made following the criteria in the general rules.
As long it is a valid QSO with exchange of callsign, reports and the activator mentioning the reference everything is fine.
3.7.1 Criteria for a valid Expedition
8. At least one QSO must be made from the Summit to qualify it as an activation.
In order for the activation to qualify for the points attributed to that Summit, a minimum of four QSOs must be made, each of which must be with a different station. QSOs must comprise an
exchange of callsigns and signal reports, it is strongly recommended that the summit
identifier be given during each contact
One exception would be a QSO within the same activation zone.
QSOs with others within the same Activation Zone do not count towards the QSO total.
It is not required that the chaser participates in the SOTA programm for the activation to be valid. It is an honor based system.
The activator sending the summit reference is strongly recommended, but not required. That is in the section you quoted. In this case, the summit reference was figured out by the chaser interviewing the activator, it seems. So still valid even if the the activator didn’t send the reference.
This also covers the case where activators send the wrong reference. That is still a valid activation.