What model and year bike are we talking about? Wheel bearing failures are extremely rare so the odds are that something was put together improperly during the tire change. Having both bearings go at the same time would make this extremely unlikely to be just a random chance sort of failure. However, proving that may be a bit of a problem. If the original dealer won't accept responsibility, or pulls some crap about having to return the bike to them, then you have to look at what it would cost to transport the bike back to them while realizing that they may still blow you off and leave you with the transport cost as well as the repair.
This is one of those situations that all too many of us run into when dealing with our friendly dealerships. A strong desire to not let them screw us says take it back and pressure them to do the right thing. But then common sense and experience say to just find a better place (dealer or independent) to handle your work and pay to have it fixed. I personally hate doing that because it feels like I'm letting them get away with something, but after years of fighting the fight I've grown weary. Now if they don't respond favorably or at least fairly to a complaint, they go on the list of places never to see another of my dollars and I go elsewhere.
BTW, if you feel like fighting and paid for the tire change with a credit card, you could also dispute the charges with the credit card company. May or may not get anywhere, but if nothing else the dealer will have to respond to the inquiry.
Jerry