First, breast milk wouldn't been produce if the woman does not gone through labour which means she must already have children and second in my religion a man cannot married anyone who breastfeed him or anyone who has been breastfeed by the same person as him even if they are not blood related
I have two theory why he is summoned
1) the demon lord try to summoned her husband candidate but instead she summoned someone from other world
2)the human kingdom try to summon their champion to go againts the demon lord but the messed up the summoning location and sent their heroes to claim him...
Sharks do not just eat human like that in fact shark are less dangerous and more approachable than killer whale. If shark recognize you as human that it would not attack or eat you so this oneshot is bullshit.