I didn't encounter "sequel" until some years after I encountered "ess-queue-ell" - had no idea what the person was on about to start with.

I guess it's one of those things that native English speakers don't even know they know. Like "Fewer tests means Less data", rather than "less tests means fewer data", or "six charming small new round green plastic tables" rather than "six plastic charming green round new small tables".

Or that "the" is pronounced "thuh" before consonant sounds and "thee" before vowel sounds - same rules as "a"/"an" but no difference in spelling!