I think they came from the air vent above the tube.

Help Please.

It's not likely that they came from the air vent. If you will attach a picture of the bugs and tell us what area your are in, we can help you identify the bug, and from there how to stop them from getting into your house or apartment.

We need a good close picture, and where you live.

The only thing coming out of the vents in your bathroom if you have no duct leaks is what goes in at the return for your unit or what has flown in the vent and died in there.

If you have a evaporative cooler then the bugs could have been sitting in the water pan and blown in when you turned that on.

Do you have an evap cooler? Even if it is decommissioned it can hold bugs, etc.