I heard back from Evelo customer service on this. Here's the answer -
I heard back from the factory on this last night. While our displays do not include a USB port (the output is so low that we decided not to include it--it just ends up adding frustration for customers), the display has the functionality to turn the USB on and off, in case it is equipped with a USB port.
Hitting the "set" and "+" buttons simultaneously will toggle this one and off. I'm guessing that you likely hit this sequence inadvertently, but if this comes up randomly in the future without hitting any buttons, please let us know.
All the Best,
John O'Donnell
Director of Product Development