What does it mean to be "t-boned" by something?
The literal meaning of "t-bone" in this context is referring to a type of traffic accident where one vehicle drives into another from the side - generally meaning that vehicle does not see it coming and can't do anything about it.
In this usage it's similar but less literal, it means to be set back by something that you don't see coming.
T bone is where your front end of vehicle goes into the side of a vehicle (mostly happens at junctions or stop signs)