Have an ATC friend, he said after a rash of incidents and near misses, they are strict on hold short instructions. While other instructions like “American 101 contact departure” can be met with a “Goodday, 101.” there is zero room on a runway hold short instruction. They need a readback of 4 things, the hold short verbiage itself, the runway, callsign, flight number. Miss any part of those on a hold short instruction, they will ask you to repeat properly.
“Nice job champ” was deserved after the pilot enunciated the incorrect “American Airlines” on purpose.