Those scenarios are very different to taking out a bank loan (which would generally be a worse debt than a student loan).
The person who said they were planning to take money from their pension probably meant from their private pension pot, which may be very large, and surplus to what they need for their own retirement. They can take out a tax-free cash lump sum when they turn 55 up to a certain amount. If they don't spend their full pension pot then it may be subject to inheritance tax when they die, so it makes sense to give it away any surplus sooner rather than later.
For the person who said they'd pay uni fees but not a house deposit, that sounds like a personal choice rather than that they couldn't afford to help with house deposits if they wanted to. She didn't elaborate. Some people are able to do both. If she hadn't spent all that money on private school fees she could almost certainly have done both. Horses for courses!
"My own conclusion was that it would be much better to put any spare cash you had towards your child’s mortgage rather than their student loan due to the fairly low interest rates on the student loan which are actually set at the rate of inflation."
If you can only afford one, and your child is on a plan 5 loan (not a plan 2 loan) that is probably a wise decision. Other people have different circumstances to you so make different decisions.
My dc1 would have had a plan 2 loan, with much higher interest than plan 5, so I'm glad we were able to help him avoid that. My dc2 would have had a plan 5 loan, but we wanted him to have the same as his brother. In both cases we will be able to also fund deposits for future homes too - putting them in the same position DH and I were in in our early twenties - debt free and able to buy our first flat.