The tools that could have been used are numerous. What you should do is try a few. Try a shag carpet, a broom, an ocean sponge or even some wadded up newspaper. Your guess on the proceedure is probably right. Possibly the tool was dipped in the mud and slapped on and pulled off. Timing is important; wait until the mud firms up some before you knock it down. If it gets too hard use more pressure. Experiment on some scraps of drywall. After you do a few tests you will figure out what works to get the right length and width and density of slaps. Are you trying to fix it with plaster or dryall mud?
