That's what I assume too.
I do routine maintenance on my X5 almost every 5k.
I've replaced all filters (air - fuel - oil) 02 sensors but NOT cats converters?
I'm constantly monitoring the engine via INPA and cannot see any anomalies on anything.
Experimented with Premium fuel (98 RON) from different service stations as well.
And for giggles......tried 91 and 95 RON!
.............and made no or little whatsoever........except lost a bit of torque down low.