2NT was unusual, 3♦ was a preference.
the X of 3♦ was takeout for the majors, redouble showed a strong unusual NT.
4♠ showed "4+ spades, 8- total points" (it had 3 points and 6 spades to the ten).
5♦ showed 29-30 points! How often am I going to have 29-30 points and settle for 5♦ with 5-5 distribution and a clear preference from partner?
For that matter, how often am I going to have 29-30 points when east opened and north is looking at 5 HCP?
GIB raises to 6 because we apparently have 34-35 combined points.
I held ♠ - ♥Kxx ♦AKQTx ♣AQxxx by the way. I only need a rounded-suit honor to make 5♦ a good contract.