well, we don't know the type of procedure or the quality and reputation of the clinic, so possibly it's justified, nor do we know if the treatment document was on letterhead with the doctors info, or just signed by a nurse at reception. I'm thinking it didn't look too professional from the getgo.
People need to be sure they have all their ducks in a row before submitting an application. Which includes being prepared to submit full documentation for businesses and owners under the soft power category.
Try the doctor's license likely displayed on the wall instead of his ID. Same for clinic business license. Include a brief note that the doctor is reluctant to not share his Thai ID card.