It is not categorically false, as evidenced by your quote which says they are allowed plainly, and as I caveate'd my statement with quotes. Perhaps we should replace "proxy" in my statement with "clones".
WOTC, judges, players, do not check for "dupe/clone" cards. How can they? why would they? To prove the player/opponent is poor in this individual set in the middle of a tournament?
When we're taking about proxies in sanctioned tournaments, we are not talking about what WotC is talking about:
No one declares at tournaments "This is my proxy" and presents a hand drawn liliana, that then prompts the inspection you quoted in which the judge has to unsleeve my very valuable card for the judge to inspect, and can only be used for the tournament. What a waste of time and lack of professionalism, for no reason. WotC would stop paper magic tournament support.
Instead they play a "liliana of the veil", in mint condition holo somehow, and we all know what's up.
Players fake/clone cards very easily/well, for obvious reasons. You would not be able to determine my commander deck is entirely "fake". There's no mechanism in tournaments to prove it. I simply don't want to support Hasbro/WotC and TCGPlayer admins.
I assure you, as a frequent bottom 2048 loser of these sanctioned tournaments, every single player is playing with clones, WotC is aware, and they would be foolish to enforce any ruling on that.