You're not crazy. It's listed 6th down in the Topaz Hall section of the Challenge page. As a Gold Member, you're only allowed to bank 75 Questions per day (this is listed on the banking page, after you click the "convert to points" button in the quick quiz), which is why you only get credit for 75. The mini, however, is for a cumulative
question banked total of 100 questions. If you go to the challenge page, you should be awarded the mini, since you have banked 150 total
Edit: Copying directly from the banked questions page:
Regular players get a pool of 100 questions every day, and may bank 20 correct answers per day (max 200 points).
Gold members get a pool of 15,000 questions every day, and may bank 75 correct answers per day (max 750 points)."
And from the Challenge page (I've already completed it, so it looks different than it will for you, but the Requirements are the same):
Awarded to a player who banks at least 100 correct answers cumulatively in the Quick Quiz game."