Not the best version of that joke I have ever heard but I love that you posted it!
This is one closer to what I've been used to.
"A man walked into a bar and sat down, and ordered a beer. As he sipped the beer, he heard a soothing voice say “nice tie!” Looking around, he noticed that the bar was empty except for himself and the bartender at the end of the bar. A few sips later the voice said “beautiful shirt“. At this, the man called the bartender over. “Hey…I must be losing my mind,” he told the bartender. “I keep hearing these voices saying nice things, and there’s not a soul in here but us.” “It’s the peanuts,” answered the bartender. “Say what?” “You heard me,” said the barkeep. “It’s the peanuts … they’re complimentary.“