I am a 64 year old Canadian living in Phrachuap Kiri Khan 20 Km from Bang Saphan.

I registered @ https://expatvac.consular.go.th/ on 2021.08.02
This is the only registration I have made for a vaccine.

 

Last night at 2100 I received a phone call from a doctor at Bang Saphan hospital.
She spoke excellent English and asked me if I had had any covid vaccinations yet.
I replied no and she asked if I wanted the Pfizer vaccine, I said yes.
I was told to come in the next day at 0900.

 

So today I get to the hospital at 0905.
Filled in 3 pages of forms mostly ID and medical condition. Got my number (10)

Took them a bit to get organized, then things began to run smoothly.
Got my jab at 0940, 
Received an appointment slip for September 14th for 2nd jab.
Left hospital at 0955.
They did not charge me anything.

 

So was this from the expatvac registration?
Hard to say, there was an official from the Ministry of Health, but I was unable to get an answer from him.
There were only 12 other Farang who were vaccinated while I was there. All appeared to be over 60.
You would think if it was due to the expatvac registration there would have been more people there or maybe appointments were really spaced out.

 

I asked some of the other farang if they had registered with expatvac, not one had, in fact they all had registered with different sites!
My neighbor who is 74, was also registered with expatvac and did get a call, but had already got Sinovac.
Another friend here also registered with expatvac is under 60 and did not get a call.

 

If this was not from expatvac, I can't think of how they knew about me. 
The only agencies that have my info is immigration and the motor vehicle department, neither seem as probable sources.

Marks, are you registered with the Canadian Consulate as living here? That is a possible vector for your info getting to the Provincial Health Authority.

No I did not Register with the consulate.

This was the national health department as far as I can tell.