In one of my posts ("that's a very good one to know" vs. "that's good to know") a nice answerer gives 2 examples and corresponding explanation
Speaker A tells a jokes, speaker B likes the joke, so he says ,"that's a good one" in response.
"a good one" means "a very funny joke". I understand this part clearly.
Speaker A announces that he's managed to fix the problem with the software, Speaker B acknowledges it by saying, "that's good"
"that's good" means "an unbelievable assertion". I don't think I understand this part correctly, so I looked it up on a dict and got
a statement that you strongly believe is true
I certainly don't agree with his assertion that men are better drivers than women.
with this definition, "an unbelievable assertion" seems to mean B dose not believe A, or at least dose not believe A strongly.
Which does not make sense. If B dose not believe A, why does B have A solve the problem and acknowledge that?
Could someone please give a hint? Thanks in advance.