Said sea creatures are actually in the process of growing legs. Wise, patient Tibetans know this. They wait and meditate for the "Great migration of sea creatures to their soup bowls" due in a million years.
Poor simple mountainfolk. They forgot their chow'll have to cross India first. Yum.
I've lived in Indian side of Himalaya for substantial part of my life and I've seen people consuming fish or whatever else is available in neraby water sources.
It depends on availability. People who live near rivers, lakes, ponds etc would include acquatic creatures in their food other won't even think about it.