I'd taken droll to mean something like drily amusing, but without any implied negativity.
But I've often heard people say
in response to something that they appear to find mildly amusing but not exactly LOL territory. They certainly would not have described the comment as hilarious or very amusing, which terms would be reserved for something much funnier.
Hacker: Who else is in this department?
Sir Humphrey: Well briefly, sir, I am the Permanent Under-Secretary of State, known as the Permanent Secretary. Woolley here is your Principal Private Secretary. I too have a Principal Private Secretary and he is the Principal Private Secretary to the Permanent Secretary. Directly responsible to me are ten Deputy Secretaries, 87 Under Secretaries and 219 Assistant Secretaries. Directly responsible to the Principal Private Secretaries are plain Private Secretaries, and the Prime Minister will be appointing two Parliamentary Under-Secretaries and you will be appointing your own Parliamentary Private Secretary.
Hacker: Can they all type?
Sir Humphrey: None of us can type. Mrs MacKay types: she's the secretary.
Hacker: Pity, we could have opened an agency.
Sir Humphrey: Very droll, Minister.
Hacker: I suppose they all say that, do they?
Sir Humphrey: Certainly not Minister. Not quite all..."
(From Yes, Minister series 1, episode 1: Open Government.)
Is this a correct understanding of the term? Does it suggest a lukewarm assessment?