Hello VW Acolyte,
This is not a typo, but you will find that if you look at European application lists, the 50mm strut is the one used on many of the MK5/6 platform based vehicles.
To use your HR preference, check out their Euro App list:
http://www.h-r.com/de/f_produktsuche.php
Put VW in the first drop down, and then Golf 5 in the second and hit
Suche
You will see that there are 2 different "Federbeinaufnahme" AKA Strut bodies:
ø50mm & ø55mm
In this case they show one of each strut size for almost every application.
I do not know their purchasing practices at VW, but it is possible they had a surplus of the smaller ø50mm shocks and spindles in their system and it was cheaper to use - I really cannot say.
Your research looks to be spot on with what we have found as well, thanks for the independent confirmation!
Let me know if you have any questions!
Glen @ AMI