There is no auto defrag feature in OS X. To defragment a drive (which should hardly ever be necessary - never for an SSD) you would have to use a third-party utility. So unless your Dad installed a utility that auto-fragmented the SSD that was not the culprit.
There's not really enough information to make a guess as to why the SSD failed; you don't even say which model of Mac it was. There have been cases of faulty SSDs in certain Mac models which Apple replaced free of charge. It is possible that your Dad's was one of those models. In any case, if it failed with only a year's usage he should have taken it back to Apple; they would almost certainly have replaced the disk free of charge.