As others have said, there's a fair bit of context missing here.
It's easy to accrue a chunky debt with e.g. essential house repairs which are unexpected and not covered by insurance or a specific loan taken out for e.g. loft conversion/extension/new kitchen. These feel scary to me but they're not that crazy, especially when the works could be adding on to the resale value of your home, or just making it more suitable for your needs (that's what we're currently doing).
It's more worrying I think if it's just built up bit by bit over time because that would suggest they're living beyond their means, not budgeting realistically etc.
My DH's always been debt averse as he's not got generational wealth, he knows there's no safety net of the bank of mum & dad, when we've borrowed or bought something on credit (e.g. a sofa), the repayments are always affordable and the thing we've bought has been good value for money.
I've still ended up with credit card debt over the years but it's always at a level where I'm affording the repayments, I've moved them over to 0% cards, minimised the interest, played the game, all that. I think it would be very easy for it to escalate if you said yes to every credit card that offered, or used store credit.
I sometimes buy stuff from Next but I'm always on top of it - like my balance is at £5 at the moment. I can see how some people could easily see "available to spend" as free money. I've just checked my account and I've got a £3750 credit limit on Next which is CRAZY!!! I've never ever spent that much.
Anyway - get them to talk with Step Change, there are other organisations too. I follow some good debt related people on instagram who are very open and honest about how they've tackled their debt.
Finally, it's a good thing that you know, that they've told someone. I've assumed it's because they know it's a problem.