@Elías *******
Regular checks does not mean that they could not concentrate these checks on a certain type of visa.
You can think of several reasons why they pay extra attention to DTV now, that does not mean they are "anti-DTV".
It is perfectly understandable that after existing a year they want to evaluate some aspects and therefore want to check how much the visa is abused.
Without checking you would not have that info.
A check in a separate room, might be because of privacy reasons.
I think in the past there were many checks on the much abused ED visa, so yes they also check other visa well known for abuses.