East asks for an explanation of the auction before leading. NS play 5-card majors, 4-card diamond suit and strong NT. 2♥ was a normal reverse* (in the English style, usually showing 16+ HCP or so, could be lighter with extra playing strength, although this wasn't said in so much detail at the table). South said about 5S "We don't play this as asking for anything in particular, it just asks me if I like my hand for slam". East thinks a bit longer and asks if it is asking for anything in particular, South says "No, it just says bid on with a good hand, it doesn't ask for anything specific" - South has a very slight stammer and couldn't get out the word "specific", North completed it and added "it's just a quantitative invite".
East led the ace of diamonds against 5S, and West (a much weaker player) played the lowest outstanding diamond. East then tried to give West a club ruff, and the contract made with an overtrick (West has the ace of hearts). Declarer has lots of solid spades, a singleton diamond and the rounded suit jacks.
Everyone agrees that the 5S bid was very slow.
After the end of the stanza, East then asks for a ruling. He says that the slow 5S bid demonstrably suggests passing, while South has an obvious slam bid opposite a fast 5S bid (I think the implication is that NS would usually play that 5S asks partner to bid 6 with a diamond control, but being slow suggested that North was looking for something else). He also says that against slam they would have cashed their two aces.
South says that (i) no-one has ever bids 5S quickly in this sort of auction so there was no UI other than North wasn't sure how to bid his hand, and (ii) that having reversed South now has an unsuitable hand with minimum HCP and in particular only one ace and no reason to bid slam.
N/S have a 33-page section of their system notes on competitive bidding, but it doesn't include jumps to 5 of a major (nor does the uncontested system file).