I'm not sure why you're surprised: this hotel is a nickel and dime property, so they want an immediate deposit on reservations. They probably "forgot" to charge the card back in February.
Agree that it's completely unacceptable practice, but many practices at this property (extra mandatory charges not in the rate, steep fee for parking at a suburban location plus lack of self-parking, etc.) are unacceptable in my book.
If you're PAYING for your stay, you may want to look at the nearby Marriott Napa Valley: although one can argue that it's a bit less refined, it's far cheaper on a total (real) cost, with no extra mandatory charges not in the rate, free parking, and no deposit requirements.