Your car’s oil pump puts out something like 6-8gpm at idle. If a filter wasn’t installed or was double gasketed, it would take about 15 seconds to pump all the oil out of the sump.

If you filled it back up with oil and there’s no filter, there’s not going to be any mystery about what’s going on.

If someone installed a 20mm threaded filter on your 3/4” Toyota, you could eject a filter while driving. You would be out of oil in a matter of seconds.

Could the oil change place screw up? Yes. Could your filter have leaked oil? Yes. Did you drive 15 miles without a filter? No. Did you add oil, start the car, and not notice the filter was missing? No.

You’re going to have to fight a real uphill battle to show that you didn’t your notoriously junk Toyota 2AZ out of oil, and are trying to run a scam on the quick lube for a new engine.

You have a petcock on the radiator.

In theory you have 4L of new coolant and 2.5L of water/residual coolant. Roughly 60:40 for maths.

If you drained 1.25L of coolant from the radiator. You’d remove .75L of new coolant. If you add distilled water, you’ll be closer to 50:50.

A smarter way is to get an inexpensive refractometer, and test the coolant. Maybe wait a week to let the coolant in the overflow reservoir mix.