The test that was met
Article 401.15 of the Criminal Procedure Code allows a cassation court to intervene only where there were substantial breaches of the criminal law or of criminal procedure that affected the outcome of the case. That is a high threshold, deliberately. It is met by things like evidence admitted in breach of Article 75, a verdict founded on material never examined in the hearing, or the denial of a defence lawyer or an interpreter — not by disagreement with the court's conclusions.
Why multi-charge cases produce these grounds more often
Where several articles are tried together, the volume of material is large, hearings run over months, and the rules on combining sentences under Article 69 come into play. Procedural corners get cut, and errors in the sentencing arithmetic are common and visible on the face of the verdict. In cases of this shape, the strongest cassation grounds are frequently the most technical ones.