This was embarrassing but in an interview I was asked if I what the current version of Java was and I wasn't sure but had an idea. I said 7 (and the correct answer is 8). In situations like this is it better not to guess and admit you'd have to look it up, or would you guess and say your not sure? I actually do know features new in Java 8 (such as lambda expressions) but the number slipped my mind. I could've answered "I forget the number but I am familiar with the newest version and features such as x y z". I know, rookie mistake.
I always answer with the truth. That's my "prime directive" in an interview.
If the truth is that I don't know something, I tell them. I would much rather have them see that I'm willing to admit that I don't know something than to have them discover through a wrong answer that I'm trying to put something past them.
When I've interviewed people, I've sometimes asked them questions I was nearly certain they wouldn't know the answer to in order to see how they would respond. That tells the interviewer something about the candidate and how they react under a stress situation as well.
I was applying for a Delphi position about 25 years ago and the interviewer asked several questions about C++. I answered him honestly that I didn't know. He later told me that he was specifically trying to see whether I'd try to BS my way through or not and also how I would react to the stress of seemingly being asked something for which I was not the least bit prepared.
I'm not suggesting that you should just say "I don't know." and leave it at that. I think your explanation about the features is the kind of elaboration mixed with forthrightness that would be the most helpful.
You should be open about you not knowing or not being sure about something.
And here is the main reason, in my opinion, for that:
If you say "I don't know" when you don't know, they will trust you when you say "I know".
Now that might look stupid, but it is not! I like a lot working with people who are open about not knowing. Actually, I find it a quality: to be aware of your limitations and to be transparent about it.
In the other hand, I don't trust people who never say "I don't know". I know as a fact that nobody knows everything, so if someone never expresses doubt I will never be sure if they really know what they area talking about, as they never "don't know".
Besides this, as my own interview strategy I try to build a connection by being human: I make mistakes, I don't always know everything, but at least I am an honest person who will not lie about what I can do.
I once interviewed a man where his answer to every question I threw at him was "I don't know, I would have to check the help files".
I recommended that we hire him and we did.
I saw his resume, I knew he could do the job, but the work was for a newspaper. I deliberately asked him questions he could not possibly know because I wanted to know if I was dealing with someone who would try to hide his mistakes, or who was overconfident.
His honesty got him the job.