Before anyone wages their sleuthing skills on vultures.....
Relevant articles at bottom
Consider what snow does and what happens in freeze-thaw cycles.
--Snow moves a lot of stuff around by its bulk movement. It shoves stuff around. Consider the huge moraines left by glaciers, but on a micro scale in this instance.
--Wind over snow can create crazy conditions, I suppose because it smoothes the snow and lowers resistance. It can send bodies flying. See the video of SAR on a mission on Mount Washington.
--Snow can be involved in avalanches. Even tiny, localized, avalanches will dump stuff far from where they start. Think about how many people get buried each year in avalanches out West and where they end up compared to where they started.
--Snow can melt under a snow field and run off downstream. A recent SAR on Rainier worked with this recently to recover a body: it had floated down the mountain in the water stream under the snow.
Then consider freeze-thaw cycles....
Have you ever noticed in New England, what was a cleanish meadow in fall can become a somewhat rocky meadow in spring? That's because freeze/thaw pushes rocks up that are under the surface. Things that are buried are suddenly on top of the ground.
On different scales, this is what happens to bird feeders on poles, house foundations, cement patios, road potholes, mountain sides, frost heaves....
Now consider that the Pyrenees receives many snowfalls, many blizzards, many squalls, many freezing rains, many melts.... That's the context where the bones evidently spent the winter.
A young climber perishes on Mt. Adams
Video:
Hiker dies at Mount Rainier National Park
Science of freeze-thaw in mountain areas:
Geological Society - Freeze-thaw