[X6S1x6Okd1st]

Skimming the paper it appears so. B-trees also require sorted data.

[bmh]

B-trees don't need sorted data. The B-tree insertion algorithm performs the sorting for you.

[infogulch]

B-trees need sortable data; GP is not saying that the data has to be pre-sorted, but that it can't be unorderable or otherwise uncomparable.