If he's been in a primary where they have focused upon teaching 'to the test' (whether SATS,11+ or Common entrance Exam is irrelevant), he might be finding that they are using phrases and expecting skills that his previous school just didn't use or develop in their kids.
It's not really just about the actual principle (useful though it can be if you need to find out the weight of 20,000 bricks that have fallen off a ship into a dock to hire the equipment capable of lifting it without buckling - or to get an elephant that's fallen into a swimming pool out), it's about developing the skills to work out what they are asking, plan how to look for the information, how to deal with issues (such as inaccessible language), how to check if what you've researched is reliable and then, to understand the 'thing' and the practical application - the point of learning that particular thing.
It's not 'get your Mum to explain it to you' - that's not what they want.
He's done part of what they expected by trying to research it - you've then gone on to try and do the next step (get to understand it).
Neither of you are thick, it's just not a way of speaking or learning you've encountered before - and I think some educators forget or aren't aware in the first place that what they do/have learned about at university is not what everybody learns by age 10 and a half - chances were that at that age, they were still presenting fully word processed essays for holiday homework, researched and typed up by Mum or Dad (and at 13 they were probably submitting five pages of Ctrl-C and Ctrl-V from Wikipedia).
I could teach my DDs about research methods at the end of Primary because I was studying at the time - the way I worded it (thanks to being an 'orrible little guttersnipe with ideas above her station as a child, but I'd had a couple of teachers who had found I was less trouble if given something to look up in the school library once I'd finished everything they'd given me to do) was What Do They Want From Me? How Do I Do That? What Have I Got? Do I Understand It? How Do I Show Them That I Understand It? Show Them.
Being able to do that first means your DS isn't relying upon the teacher to tell him everything - he's developing the skills to not have to rely upon somebody else to tell him what to remember, to understand and apply concepts without having to rely upon somebody to hold his hand throughout. And, in time, to be able to work out who is bullshitting him.
Trouble is that some of the people saying 'flipped learning' is THE way to teach aren't explaining the Point (or What They Want) themselves.