Am I right thinking that it is NOT relevant for the tokens based on
mathematically reversible cryptographic functions?
You're right. But you may not want to do it that way.
Tokens are generally isomorphic to card numbers (15-16 digit numeric) because they are supposed to be able to easily replace card numbers in whatever software the recipient uses.
If you were to use tokens that don't look like card numbers, than you've "provided a mechanism for distinguishing between tokens and actual PANs."
4111111111111111 is distinguishable from
But tokens are usually generated by a processor or card brand and handed to a merchant for use instead of card numbers, usually using programmatic interfaces that were designed and specified to communicate 15-16 digit numbers. The merchant probably already has software, with a database and application logic and everything, that was designed to store card numbers. When they tokenize, they have to start storing tokens instead of card numbers. If the tokens look enough like card numbers, then it's usually a simple non-disruptive switch. For "distinguishing [between these isomophic] tokens and actual PANs", they might use invalid IIN/BIN numbers, fail the Luhn algorithm check, etc. etc.