You can read more about the ponies on the Society website that preserves them: https://www.eriskaypony.scot/gaidhlig
Why are Eriskay horses famous?
Eriskay ponies a rare, native breed of pony from the Hebrides. :)
Because they can recognise tourist/hire cars from the local ones and place themselves at strategic angles on the road, refusing to budge so that the cars can't pass & miss the ferry to Barraigh ;)
I don't know that they're terribly famous. They're kind of a smaller and lighter version of the Highland pony, but they're pretty well always grey as opposed to the wide variety of interesting shades the Highlands come in. Nice ponies.