In eQuest, outdoor air and exhaust air requirements specified at the zone level take precedence over values specified at the system level. So, although you tried to make your system 100% OSA with the system input for MIN-OUTSIDE-AIR, this is being ignored due to your input of an exhaust flow at the zone level. From the help (right click on field) for MIN-OUTSIDE-AIR:

If you enter MIN-OUTSIDE-AIR as well as the ZONE keywords OUTSIDE-AIR-FLOW, OA-CHANGES, OA-FLOW/PER or EXHAUST-FLOW, the ZONE values take precedence.

So, to correct: you should specify that there is 100% outside air flow at the zone level probably by specifing OUTSIDE-AIR-FLOW in cfm for each zone.

Also note:

• The unit ventilator system type does have a return air path, but it does not have a return fan, so I think you will be modeling your described actual system just fine.
• The unit ventilator system is a zonal system, so to confirm the system is operating as desired use the thermal zone hourly report variables, where you can report zone unit system supply cfm, zone exhaust cfm, and fraction of OSA to supply air for the zone unit. system. Additionally, if you have multiple zones assigned to a single system you will be simulating one unit ventilator per assigned zone.