It’s a oversized variation of a vacuum break a’la PVC piping but the vacuum break is normally above the sink bowl. Hence the system is probably not what the MFG of the dishwasher had in mind. The MFG installation instructions should be the guide first with the AHJ modifying it as they see fit.
That would be after the air gap or backflow preventer. . .
P2717.1 Protection of water supply. The water supply for dishwashers shall be protected by an air gap or integral backflow preventer.
**P2717.2 Sink and dishwasher. **A sink and dishwasher are permitted to discharge through a single 1.5-inch (38 mm) trap. The discharge pipe from the dishwasher shall be increased to a minimum of 0.75 inch (19.1 mm) in diameter and shall be connected with a wye fitting to the sink tailpiece. The dishwasher waste line shall rise and be securely fastened to the underside of the counter before connecting to the sink tailpiece.
Actually Tony, I just remembered, CO code is based on the UBC (UPC in this case).
UPC 807.4 No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the use of an approved dishwasher airgap fitting on the discharge side of the dishwashing machine.
This is actually a correct installation, I don’t like it either but is “up to code” The design is in place of a typical air gap one would see at the top of the sink. The open end on th “y” is the air gap which ensures there is no cross connection of waste water going back into the dishwasher. I would like to see the open ends above the bottom of the sink in case the drain backs up and call out if it is below the sink.
Hope that helps, you’ll see alot of these in newer homes.