If I understand you correctly: you’re stating that the class ‘hidden-xs’ should show content on small screens, am I correct?
When we take a look at the code:
the class hidden-xs applies to media devices with a max-width of 767 px and it would indeed mean that every element that has this class will not be shown on these devices.
This is an example from a Mendix 8 project, it may varie for other Mendix version.
I hope this helps you, if not: feel free to provide feedback.