North-South, not a regular partnership, were using predominantly natural methods including old-fashioned Blackwood.
Some would have responded 1♥ with the North hand and the 3♥ rebid seems an overstatement. South, who regarded the 3♥ bid as forcing, was perhaps a bit impetuous with his 4NT bid: could partner have had KJxx Axxx KJxx x for his 3♥ bid?
Finally, it seems a bit odd that South didn't bid 7NT which was known to be iron-clad facing four aces and heart support.
Plus... it's free!