Qualcomm needs to know if a vendor is lying about the number of chipsets it has used. They need to know if the vendor claims 10M cheapo handsets and 1M expensive handsets - they need to know if the numbers are actually reversed!
This backdoor can get them the evidence they need to invalidate a license with a vendor - cut of chipsets shipments - and start a new negotiation. Remember, Chinese vendors will cheat like bananas. Chinese vendors asked for a HUGE discount on domestic phones - and they go it - but at the cost of a higher-than-normal royalty for exports. They are probably cheating, it's what they do.