Bank of America booking is more expensive than regular

I’ve been booking my stay for a trip to Japan, and I noticed a trend. When using Bank of America you have the option to go to your rewards and use their 20% of booking option. I selected Booking.com through my regular browser and Booking.com through the Bank rewards browser. Every time I used it the Bank’s browser, it charged more than the regular browser. Same hotel, room, amount of people, day. Is Bank of America gaslighting their customers?