The owner didn't modify that car. Dodge (Stellantis) did. The owner chose the mid muffler delete option when he ordered the car. Said so right in the article.
But it also says the mid muffler delete isn't why the claim is being rejected...
He says the mid-muffler and entire emissions system are stock. But this is where things start to get confusing. You see,Dodge says this isn’t about the mid-muffler. Dodge says, “The warranty claim was rejected after a Stellantis Calibration Engineer ran Powertrain Control Module (PCM) diagnostics and confirmed that the vehicle’s PCM was tampered with and contained non-factory software.” A spokesperson added, “I haven’t seen anything on our end regarding mufflers (ie not the issue).”