Old bridge maxim: all 7-4 hands should be bid to game unless there is a compelling reason to suggest a misfit. This goes double for 7-5 hands. Further, you should normally play in the 7 bagger since you usually need trump length to stand the taps. 7-5's and 7-4's are not really two suiters unless partner has 4 or 5 card support.
After two passes (not everyone's choice, but reasonable) the next two hands advertised balanced distribution (1NT and double). The East hand: you don't have to be Sherlock Holmes to deduce that if you are 7-5 in the majors, LHO is loaded in the minors. The South hand knows RHO is mostly majors. Both East and South can tell that the HCP's are split about equally.
Further bidding by both East and South should be aimed at buying the contract as cheaply as possible. The straightforward approach would be for East to bid 4
♥ and South to bid 5
♦. After pass-pass, East should bid 5
♥. 5
♥ doubled down one would likely be the final contract.
East might get cunning and bid only 2 or 3
♥. South probably ought to jump in
♦, either bidding 4 or 5. On the actual bidding, South was the chump who forgot to bid 5
♦ at the appropriate moment. South 100% to blame.