Don't know why the datasheet drawing has a square "hole" outline, but the dimension is correct.
The protruding body is listed as 1.4 x 1.6 mm.
The diagonal is sqrt(1.4^2 + 1.6^2) ~= 2.1 mm.
So a round hole >= 2.1mm will suffice. Probably 2.6 would be a good idea? If you want to route that for a little better straight-sidedness on the hole, you can, but you'll probably incur the cost of a route (...which probably isn't anything, and if your board outline is already non-rectangular, a rout process is required, regardless).
Tim