This is either a rumor, or they had agreed on separation of property, or a prenuptial agreement, or he had already brought corresponding assets into the marriage. In a classic community of accrued gains, both are entitled to half of the total accrued gains.
Exactly that is the case.
Regarding the topic of accrued gains and the house. One should be aware that the accrued gains only include a
monetary value, but not the transfer of ownership! This means: If the wife alone owns the house built during the marriage, the house belongs solely to her even after the divorce. The husband then only has the right to half of the accrued gains, which can
MAY be, for example, half of the property's value, since accrued gains include all assets (final assets - initial assets = total accrued gains), which means that theoretically the accrued gains can be a completely different value than the property's value. The husband does NOT acquire ownership of the house through the divorce either. For example, the man cannot decide together what happens with the house, whether it is sold, who stays in it, etc...
EDIT: This happened with my parents-in-law. The father-in-law was given the plot of land as a gift from his parents; the house was then built during the marriage. However, the father-in-law was solely listed in the land register all those years, although the mother-in-law was, of course, also properly included in the loan contract and had paid off the loan together all those years. After nearly 30 years of marriage, the mother-in-law gets a divorce and experiences a nasty surprise because she is not a co-owner of the house but only receives half of the accrued gains. She was not aware of this all those years. She assumed that she could keep the house after the divorce. But it doesn’t help; she had to move out, and the father-in-law stayed in the house. That’s what can happen if you don’t properly inform yourself and ensure that you are listed in the land register.