You can read the background of this flag in https://github.com/kkapsner/CanvasBlocker/issues/290

To be short: this flag makes you 100% unique and trackable across all domains. The use case for this was not to prevent fingerprinting but to disguise. Not quite the main focus of CanvasBlocker but it seemed useful for some folks.

In general I highly discourage you to from using this flag unless you clearly understand it and it suits your need. If you use it you have to reset your persistent random number generator quite frequently.

PS: domain x cannot request any additional data from domain y but the faking will add the same "randomness" to the API readouts and this information can be used to be tracked.