That's not what fragmentation means. Nothing wrong with the query or the accuracy of the column, just the interpretation.

Fragmentation is a measure of what percentage of the pages in the index are 'out of order'. Out of order being where the logical order of the index (as defined by the index key values) and the physical order of the index within the data file are not the same. So a high logical fragmentation tells you nothing about what percentage of the pages are full of data, it tells you what percentage of the pages in the index have a physical order that doesn't match the logical order.

With a fragmentation that high, I would suspect there's some database shrink operations?

To see on average how full the pages are, you need to look at the avg_page_space_used column.