What makes Hidden Tideturner ignore hidden restrictions?

Tideturner is able to ignore the standard targeting restrictions for cards played from Hidden because its ability possesses a specific targeting requirement that cannot be fulfilled by units at its battlefield.

According to Rule 811.1.d.2, while choices made for cards played from Hidden are generally restricted to the battlefield where the card was hidden, an exception is explicitly provided for this exact scenario:

"If a hidden spell or a play effect of a hidden permanent chooses any targets, those targets must be chosen from among options at that battlefield, unless the ability explicitly restricts targeting in a way that makes this impossible."

The rule explicitly cites Tideturner as the example of this exception:

"Example: Tideturner is a unit with Hidden and “When you play me, you may choose a unit you control at another location. Move me to its location and it to my original location.” Because its play ability has a targeting restriction that can never be fulfilled by a unit at its battlefield, its target may be chosen freely from among the available options."

In short, because Tideturner’s ability requires you to choose a unit "at another location," it is physically impossible to fulfill this requirement if forced to choose a unit at the same battlefield where it was hidden. Therefore, the game allows you to choose targets freely from other battlefields.