Unless the language says "suggested" then it is not to be considered as a firm offer. Also if they are showing you a range of APR's opposed to a single APR then it is most likely a suggestion based on the cards that you were interested with. I don't have a BofA card yet, but I have been receiving Pre-Selected offers from them by mail and all of them have a single APR with an annotation "This is a firm offer for credit" you can continue to visit their site for offers and that might trigger them to send you an actual offer by mail.
Most of the time when you go to Boa's prequal site, its usually not very reliable. What card are you interested in?. Uhm, cashback. Ok. We think you'd like our cashback card. Really, lol. Ymmv on that site
