Skeletons deal damage to players, when submerged in flowing water in a narrow one block space when the player deals damage to the skeleton.

While I was playing Minecraft in a cave in the deepslate area, near a stream of water flowing from above, I attacked a skeleton trapped in the cave.At first I thought I took damage from attacking the first skeleton because the first Skeleton was wearing a chainmail helmet enchanted with a thorn enchantment. But when I attacked the second Skeleton, in the same spot, I still took damage, even though the Skeleton wasn't attacking me. The video I attached below is Video Evidence of me attacking the Second Skeleton.