This rule is a house rule, because any rule that involves putting any amount of money under Free Parking is a house rule. As @Joe W quoted:
"FREE PARKING": A player landing on this place does not receive any money, property or reward of any kind. This is just a "free" resting place.
-The Rules of Monopoly (1935), p. 6
It is understandable that you would end up with a house rule like this (or any other house rule), though, because the 1935 rulebook has no diagrams, is rather dense, and, IMO, is poorly organized. After acquiring Parker Brothers and thus Monopoly, Hasbro has attempted to rectify this problem in newer editions of the game by rewriting the rulebook from the ground up, keeping the actual rules the same, but using more modern language, adding diagrams and figures for every major concept, and ordering concepts in a more visually intuitive way - for instance, this rulebook that comes with modern editions of Monopoly Classic. These new rulebooks, either next to or in place of the 60-90 minute "Short Game Rules", also contain explicit advice against using house rules, giving a few examples of very common house rules and advising that they usually make the game last longer:
To keep games short and sweet, don’t use house rules!
Always auction when someone doesn’t want to buy the property they’ve landed on.
Never loan money to other players or make deals not to charge each other rent.
Never put cash in the center of the board; you don’t get a bonus for landing on Free Parking!
-Monopoly Classic Rules (2017)