I suspect that it's based on your balance on Dec 6th based on a related clause in the terms and conditions (BOLDING MINE):

T&C
This Offer is available to IHG One Rewards members for qualifying purchases of IHG One Rewards points made during the period from 12:00 AM ET December 16, 2024 and 11:59 PM ET December 31, 2024 inclusive (“Offer Period”). A member may only make a singular points purchase under this promotion. Purchased EQPs (Elite Qualifying Points) will count toward a Member’s Year-To-Date EQP balance. The Member will have the opportunity to either maintain their current status or upgrade to the next tier. The Member’s purchase level is dependent upon their current status as of December 6, 2024. If the Member purchases enough to cross the Elite Qualifying Points thresholds to maintain their status, that status will be granted automatically. EQPs will be awarded upon completion of the transaction, and new elite status will be reflected within 5-10 business days after the purchase. Renewed and Upgraded status gained from the purchase of EQPs will be valid for the remainder of 2024 and all of the 2025 calendar year. EQP points and resulting status will be awarded to the recipient of the EQP purchase only. Price includes all applicable fees. EQP Points are not refundable and are applicable toward all IHG One Rewards redemptions. Elite Qualifying Nights are not part of this offer and cannot be purchased. This is an exclusive, non-transferable offer for intended recipients only and may not be forwarded. Offer is subject to change. Offer cannot be combined with any other offer.

If fraudulent activity is suspected, IHG reserves the right to withhold status level pending further investigation. Final determination of a member’s eligibility to receive the status level is at the sole discretion of IHG based on the findings of the investigation. Please allow up to 72 hours for points to post and appear in the recipient's account. All other IHG One Rewards Membership Terms and Conditions apply.

For purposes of the Offer, the required Elite Qualifying Points balance required to maintain or upgrade member status is the number communicated to the member in the Offer and may not be contested by a member.

Mastercard, the silver circles design and World Elite Mastercard are registered trademarks of Mastercard International Incorporated.

The Contactless Symbol and Contactless Indicator are trademarks owned by and used with the permission of EMVCo, LLC.

Most hotels are independently owned and/or operated. The above service marks are the property of IHG® Hotels & Resorts.

IHG One Rewards terms and conditions apply. For complete program details, visit ihg.com/terms. Benefits and rewards may vary by region and are based on availability.

JPMorgan Chase Bank, N.A. Member FDIC

Save 20% On Points Purchases: Save at least 20% on points purchases when you pay for those points with your IHG One Rewards Premier, Premier Business or Traveler Credit Cards. Point purchase amounts are subject to change by IHG One Rewards. Upon completion of the points purchase, you agree that the total dollar price of the points, minus the discount, will be immediately charged to your credit card. The cost for the points purchased is non-refundable. Point purchase transactions managed by Points.com.