I did get a similar impression that was their mooted intention. But £10k isn’t nearly enough to cover a deposit and buying/moving costs to buy a house in most of the U.K. They would have to bank it and add to it, meanwhile it will be temptation.
I think they know most 30yr olds will likely spend the money really quickly, injecting cash back into the economy. The economy is suffering because most people are scrimping and cannot afford eating out, shows, cinema, activities, holidays and so on. So £10k to each 30yr old will mean lots of young people spending. Many will spend all of it on a needed large purchase-say a car or a wedding or to have a baby. Even those who don’t need and aren’t saving up for something large now and are responsible would be tempted to spend half on luxury items- like a new phone/laptop/hobby gear/cosmetic procedures/ and then might put half into savings.
I think this may be like a variation of Sunak’s Eat Out to Help Out - the government gave restaurants and pubs 50% of whatever people spent on food eating out. The idea was to inject money into the economy by encouraging spending. This is of the same ilk. Give a bit of money, to young people of an age to be high consumers knowing most will have spent all of it within a year.