GIB got itself into a lot of trouble here, bids could be better defined --
not sure what 3s vs. say double on the second round should show. Maybe double shows extra heart length, 3s shows some unspecified strong hand? In any case I don't think 3s should guarantee diamond fit as the explanation shows. Can't East just bid a minor here?
Whether 4H is OK depends on strength/hand type that 3S shows. 4H shouldn't show 3+H, should show 2, which probably affects East's later 5H.
4S is pretty questionable, 3H having already shown everything. Extra trump, but totally flat hand and opps may not have fit.
5H seems induced by 4H explanation. If it can't find a way to defend at least it should get to a minor down 1 than 5H down a lot.