I think that is the best advice I can give to anyone sitting in an interview.
An interviewer who doesn’t find the edges of your knowledge isn’t doing a great job. You are not meant to know everything.
“I have never seen that”, or “I’m not completely sure” are much better answers than bullshitting you interviewer. Don’t fake it. But the best answer you can give is, “I don’t know but …”
The gap in your experience is fine. Recruiters don’t really know what you do, they tick boxes, but the interviewer is someone who you will work with or for. They want to see how you think and how you solve problems. We hit the gaps in our knowledge everyday on the job, what we need to prove is that we can fill the gaps on the fly.
So, “I don’t know, but I think ….” goes a long way.