It's reasonable that the father was the contributor, although the father most likely did not have full Fragile X syndrome, he was probably a premutation carrier. FXS is caused by a genetic mutation where a CGG repeat extends past 200 repeats (normally it's less than 45). But some people have a CGG repeat between 55-200, that usually makes them appear otherwise “normal” (but are often affected by emotional problems and are at risk of developing a condition called FXTAS when they're older), however when they pass their X chromosome to their offspring, the repeat can expand to +200 - thus, their offspring develops full Fragile X. This sperm bank definitely should have screened their donors for the premutation, judging from this, this situation definitely seems like it had a legit case in court.