I bet those tablets had their slicer software on them.

A 3D printer is a CNC machine, it doesn’t understand 3D model files, you have to give it a series of gantry movement instructions, usually in G-code format. G-code has to be written for the individual printer it’s being run on, because some of them consider the bottom left edge of the bed to be the origin, some the bottom right, some the center, you need to know the nozzle size, things like that. So you typically slice your model right before printing. And yeah I’m not really aware of any tablet friendly slicer software.