There's a possibility that they never realized they landed on the Engines
I doubt anyone here has ever landed an A320 without gear , except perhaps in a sim , but having had this unfortunate experience on a GA aircraft , I can tell you you cannot miss it ,the lower than normal position on touch down , lack of suspension makes the actual landing quite harder , the faster deceleration with vibrations and the noise...
I realize the main gear on an A320 is not that much higher than the cowlings, but still with a few hundreds landing under the belt on the type you should notice the difference, OK, a hard landing can be the same as on wheels and not sure if the eventual pressurization remaining would suppress all that noise, but the vibrations caused by the scraping should be felt and the deceleration quite abnormal..So I doubt they did not notice..