Here, too, the subtleties of language are important in understanding how questions are answered. The Catholic Church maintains, for demonstrable reasons, that we possess the fullness of revealed truth and the full means to salvation given by God. We hold this in distinction to other denominations and religious traditions, which may have elements of the truth, but are lacking the fullness of these and are usually admixed with error. 
 
That said, we do not claim to know everything there is to know about God. God is more glorious than everything we could ever say or know about him. 
 
It is perhaps in this vein that the priest wrote his remarks. Nevertheless, one might wish for greater precision from the good father, as your puzzlement demonstrates.

Yes, Malachi 3:8 says Will a man rob God? Yet you are robbing Me!...In tithes and offerings.….Bring the whole tithe into the storehouse, so that there may be food in My house, and prove Me herewith,” says the LORD of hosts, “if I will not open for you the windows of heaven and pour out for you a blessing until it overflows. 
 
Further, in the New Testament Jesus references tithing when he says, Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices--mint, dill and cumin. But neglect weightier matters of the law--justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former. (Matt 23:23) Note that in this text, while the Lord speaks of weightier matters than tithing, he says regarding tithing, that we should not neglect it. 
 
The Church does not require an absolute adherence to the biblical tithe, (i.e., giving one tenth of income to the church), nevertheless, there is a precept that Catholics contribute to the mission of Church. While details are left to the individual conscience, tithing is a long and ancient tradition. As Malachi 3 says, tithing is not merely an obligation; it also opens the doors to many blessings.