A couple of things here.
This wasn't the only prank call he made. It was a couple of other players, also. The fines aren't because feeelings got hurt. It's the NFL setting a precedent because it dips its toes into tampering, etc.
Also, the Falcons have somewhat of a history of snafus like this (artificial crowd noise being pumped into the Georgia Dome, Arthur Smith getting dinged for injury report shenanigans, the tampering charge from last year thanks to that idiot Kirk Cousins mentioning he had a phone call with the head trainer during the illegal tampering period), so these fines have more to do with squashing future similar incidents than it does with hurting the feelings of anyone.