2 quarts low might cause the oil pressure light to come on at a stop sign or idling at low rpm, but if you got a significant engine knocking sound and a steady oil pressure light while driving on the road, most likely you were more than 2 quarts down. There’s no benefit to the shop techs to tell you that of course.
No matter where you have oil changes performed mistakes are possible. The tech may get a phone call in mid-stream and forget what they were doing when they return, etc. So good idea to check the dipstick yourself before leaving the shop, and that there are no obvious leaks under the car; then again when you get to your next destination, and once more the next morning. I know it seems like if you pay to have the job done by a professional shop or business who offers the service you shouldn’t have to check their work. But alas, you do.
I think the business owner would appreciate to know their techs are not checking the customer’s dipstick before turning over the keys.