Is "most superior" correct?

Yes, most superior is incorrect: English forbids double-superlatives.

That's because superior itself is already an absolute superlative form (well, or absolute comparative; in any event, it is already inflected by degree).

It's like using more or most on better or best. These are therefore all wrong, and sound ungrammatical to the native ear:

• *more better
• *most better
• *more best
• *most best
• *more superior
• *most superior

Superior can be used in an absolute sense, meaning either 'pre-eminent' or 'snobbish'. If used so, it can obviously have a comparative and superlative: there was a verse in Punch about one of the Viceroys of India, starting 'My name is George Nathaniel Curzon/ I am a most superior person'. I think your author is trying for this and failing. (For what it's worth, I also took it as 'more better' when I read it.)