Superstition and supernatural do NOT equal "religion". He was appalled at them abandoning rationalism because of him.
And for a man like Picard, abandoning Rationalism is a horrific fate.
Precisely. To say it in religious language, Picard was nothing but a false idol.
What I liked is that he dared to step in front of a bow to convince them that he is not a deity. Sure, he knew that he will survive but it nonetheless takes quite some guramba to step in front of a bow.
The episode neatly showed how hard it is do undo cultural contamination, even in the case of Vulcanoids.
I think it's be interesting to do the episode with a lesser captain or a hypothetical Starfleet in which the Prime Directive is merely a minor rule. You can easily imagine the deified captain considering how he could use his position in order to help the Mintakans and how these good intentions turn our horribly in the end.