I agreed with htb and azepineoo.
Moreover, I don't like the facts that the BPG agent responded to my claim with an attitude by reiterating me without (seem to me) thoughroughly verifying and validating the facts/info. I provided her. She wrote:

"We would like to reiterate that the clause 1 of the Best Price Guarantee's Terms and Conditions specifically states that in order to qualify, guests need to "Complete a valid room booking with the lowest available price (room rate) on any IHG website for any IHG branded hotel using the “Best Available Rate Search." Since the MaileSky Court Honolulu-Waikiki is not yet an IHG branded hotel, your claim is not eligible for the Guarantee."

She makes me feel stupid and I really don't appreciated that. So, I responded:

With this experience, I found it hard to believe that your company is a “service-oriented company”. If IHG takes my “comments seriously”, then I should see their practices for honesty, customer-hearted and consistency is transparent in this situation. Honesty??? How so? Please explain to me why IHG accepted a reservation for the same hotel and given their IHG BRANDED Rewards status member a discounted rate at Maile Sky Court hotel. Aren’t your Rewards system should only apply to IHG PROPERTIES??? On one hand, IHG denied my claim because the hotel is not BRANDED IHG hotel. On the other hand, it recognizes Maile SkyCourt is a BRANDED IHG hotel, and so its Rewards Club members can get the IHG perks and benefits. I find it very unethical and unacceptable. By the way, thanks so much for clearly “reiterate” to me that “Maile Sky Court Honolulu-Waikiki is not yet an IHG branded hotel, your claim is not eligiblefor the Guarantee” - “not yet”?, both Club member and non-Club member reservations took place within the similar time frame.