I was a lead of an Agile-ish dev team for a couple years. The environment was pretty informal, and for me I would understand either of the statements you're giving as the same thing.
What communications did arise regarded the following:
- If a tester says, "It looks fine," do they mean "It looks fine so far but I'm still testing" or "I finished all test cases" or "I finished the first set of test cases I was focusing on so that's all I'm thinking about, even though there's a lot of other test cases that need to be covered"? Similar miscommunications arise when e.g. there's 3 apps and a DB deploy required to finish a feature and the tester has only covered some of those, but the manager's asking about all of it.
- Are the manager and the tester on the same page about the expected scope of testing and what is/isn't critical to test?
If you're working with a very new or very-unfamiliar-with-software manager, then the difference between "it works" and "it seems to be working" might possibly need to be explained re: what software testing can accomplish, but the bigger question is whether you're answering the question the manager is asking. And I think you might not have this question if you and the manager were on the exact same page when it comes to what exact testing is being performed, because otherwise you could just say that your test cases worked without wondering if they thought you were over-promising on how defect-free the software was.
Kate Paulk's answer above has a really methodical way of breaking down what's going on, but for an informal conversation IMO it would probably be better for you to ask the manager what they're most concerned about and tell them what you have and haven't tested related to that.