Einstein's theory never actually said things couldn't go faster than light. It said things *with mass* couldn't be accelerated TO the speed of light or slowed down to the speed of light (if the object was somehow already traveling faster than light.), for it would take an infinity amount of energy to do either. Objects without mass (photons, gravity waves/gravitons, tachyons) can travel at light speed.
One thing I always appreciated about Einstein was his willingness to admit that he didn’t know everything. He was a true theoretical scientist who didn’t accept things as fact until proven.
He believed that gravity bent light but spent years seeking proof. (Many others also sought and provided proof)