Quite strange, i think this is a mistake because i mesure it by myself on several 999 and the original fork is a 53 (up) / 51 (down)
the 999 S already have a special lower triple clamp to put the ohlins standard fork for 999 in 53 / 53 .
This is the same triple clamp on a 999 S & 999 R.
Only difference is the lower part of the fork, 999 R got the radial calipers when 999 S got the "standard" calipers.