[Tsiklon]

This seems to hint at a more fundamental difference in approach.

The grandparent comment is saying that the conductors should check for student IDs to validate that the passenger is travelling with correct authorisation.

Your comment indicates that because they have the ticket they are automatically authorised to travel.

In the U.K. as an example, if you’re travelling with a student (or other form of discount) ticket but cannot produce the corresponding ID card proving this, in effect you are not authorised to use the ticket and thus subject to a penalty fare, or a fine. This makes it so that eligibility must be validated simultaneously with inspection.

Not verifying eligibility at the same time as inspection means that an ineligible user may be inclined to obtain a ticket from an eligible user.

Different systems, different attitudes.

(Of course in the U.K. a flat reduction in ticket prices across the board would ameliorate the likelihood of this occurring in the first place, but that’s secondary)