Reddish fluid sounds like they put automatic transmission fluid in your CVT transmission. Don’t drive it anymore. Call the shop to confirm the color of their CVT fluid. Most often it’s a lightish green. If they confirm this, have them tow the car back and flush the fluid multiple times. That greyish part you mention makes it sound like the damage is already done, so they might be on the hook to replace your transmission.

If you paid for a flush, they likely used a machine to exchange the fluid. Very few shops will replace the filter with these services.