Any seat in Biz shows on a KL boarding pass as "C". This does not mean it is booked in a C fare bucket. They do the same in coach. All boarding passes show Y, even if you bought a heavily discounted fare. What matters is what the receipt says, and likely it is still a coach fare with an upgrade designation.

For the OP, the KLM screenshot shows a 074 number but it is not a ticket number, just an electronic receipt number, otherwise it would have shown on the boarding pass (boarding pass still has 006 as someone else noticed) So the amount paid was a seat fee, not a buy-up to an actual J fare and unfortunately not eligible for extra MQM

DL for a while had issues with domestically selling FC GAP fares as coach with instant upgrades and then refusing MQM bonus, even though it was nearly impossible to tell at booking if a fare was actual F or "coach+". That seems to now be all in the past with bucket realignments to CDIZ.