Sounds like you pulled out in front of him after not coming to a complete stop at a stop sign. It is your fault.
Fifty feet at 45 MPH is not a lot of space. It takes about 140 feet to stop an automobile at 45 MPH. Some argue that motorcycles can stop faster due to their lower mass but being on 2 wheels makes a panic stop that much more difficult. Plus not all bikes have ABS making a safe panicked stop even more difficult. Even if he could safely stop in half the stopping distance of a car that is still 70 feet plus.
Next time come to a complete stop at intersections that have no stop sign or light on the cross traffic or next time, it might be a truck that you didn't see and you are not going to get the chance to ask about it again.
Please be safe.