"Wrongful gain" is gain by unlawful means of property to which the person gaining is not legally entitled.
A person is said to gain wrongfully when such person retains wrongfully, as well as when such person acquires wrongfully. A person is said to lose wrongfully when such person is wrongfully kept out of any property, as well as when such person is wrongfully deprived of property
This section means that you acquire something wrongfully, for example you concieve someone into selling them an article worth Rupess 10 for Rupees 50, that is wrongful gain
It means when someone loses their property by unlawful means; For example some goons forcefully taking Mr. X bag of jewels, that’s wrongful loss.