This source suggests any action which causes a monetary loss to everyone does not affect your partner. Is this true?
If you are playing by the official Cities rules, it clearly states
When a player puts in play a card which causes a monetary loss, the player’s teammate must also pay that loss.
The thread you are referencing is talking about differences between the official rules and some unofficial team rules, stating that in their unofficial rules, the teammate does not have to pay the loss.