Insurance is only pronounced insurance

Early in the film 'Marnie', Mark tells Marnie that "insurance is only
pronounced *in*-surance in the south .. which is where you're from".

Later in the film, Lil tells Mark that she can be a good guerilla
fighter and intelligence agent for him if he needs .. to which Mark
corrects with "ah ah, *in*-telligence agent".

In the first instance, Mark is showing Marnie that he sees through her
disguise. What's the point of the second?

Surely, Mark knows where Lil is from (and knows that Lil knows he
knows, she being his sister-in-law after all) .. so is he merely being
patronising for the sake of it? Or is it maybe an ego thing .. i.e. is
he displaying annoyance at Lil for knowing more about Marnie than he
does?

Fergal #.