The cataract surgery does put a little stress on the eye with some movement of the lens capsule, zonules, and iris and fluid entering and leaving the eye with sometimes large fluctuations in intraocular pressure. Any of these things can lead to a retinal detachment and it is fortunate that the actual detachment risk is so low (but not for your unfontunately.) The risk is generally around 1 in 500 to 1000 cases. It is also possible that you had a hidden, very difficult to see, small retinal tear in the far periphery, that got larger after surgery. In the end, it is nobody's fault usually, it is just one of the things that can rarely happen after eye surgery.