While I do agree with you it becomes very clear that the class is called economy extra...

SK has done a very smart move by actually using the top two booking classes for Economy (Y and S) to be seated in a separated cabin with better service etc. They allow booking in any GDS (compare BA in whose case you can only book WT+ using ba.com or a TA).

The Y-class price for LH on that route is the same as SK (more or less) so why should you be placed in Business class?

BUT, SK needs to be very careful in those cases as they have lured a bunch of customers to their own metal having this Economy Extra class. The lack of airplanes causing havoc to the schedules all the times will eventually lead to lost trust from the customers who has bought Y or S tickets specifically and they should at least offer some sort of upgrade option for a small fee to LH C class.

Regardless of which you should be able tom claim the original 150% points + tier bonus wether they put you on LH or TG.