I think she slipped her doctor's name once, Doctor Shi...I'm not completely sure the spelling, but from the sound of the name and also the tid bit of his voice that we were allowed to hear, I got the impression he may be of Indian descent. This is purely speculative, but did he say he would take care of her as a sister and express more affinity due to the ethnic connection?
From my experience, when I am traveling abroad and come across someone sharing my ethnic background, there is an instant connection, quite a lot of extra friendliness and of course speaking in our common mother language which reinforces the sense of closeness and trust.
Maybe he was extra nice to her, he could have spoken a few Indian words to Amma for example which really helps lighten up any mood (could explain why Amma's face lit up so much right after his visit, when obviously he could not have said anything substantial not having seen her bloody scans yet).
Could this bit of friendliness have stoked unreasonable optimism and a sense that he would do anything for her and be their superhero? Just a passing thought....please correct me if Sri Lankan and Indian backgrounds are completely different, as I am quite ignorant about this.