She clearly knew the right answers and was deliberately erring to make Sam feel better about himself.
At the end of that exchange, she stands alone, smiles, and says “ If ignorance is bliss, this is Eden.”.

Thanks for agreeing with me, Buderick.
RIP Gene Wilder. One of the funniest people of all time. RIP Robert Vaughn

Diane would never make herself look less intelligent under any circumstances. She got it wrong and Sam made her look an idiot. Loved it.

Well, that might've been the script writers grammatical error in that case.
RIP Gene Wilder. One of the funniest people of all time. RIP Robert Vaughn

No. She doesn't know as much as she thinks
Exactly; during the episode where she yells Sam's name while making love with Frasier she makes grammatical errors while talking to them both later in Sam's office: she says "between you and I" and then when comparing the two she says ".which one I like most" (rather than "more").
she's not as 'educated' as she thinks she is.

No. She doesn't know as much as she thinks. Sam correctly corrected her, then gloated with Coach.
Movie Theater: Young Frankenstein 10/10. RIP Gene Wilder. One of the funniest people of all time.

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