I believe that the GIDS at the original gate was not updated because it's pretty common for those to be wrong when changes happen, but I find it hard to believe there were no announcements made across the PA or the screens in the airport weren't updated.
It's a tough lesson to learn, but ultimately it's up to the pax to know when and where they need to be. Obsessively checking the app or checking the boards in the airport, and getting to the gate in time for boarding to begin, and not 15 minutes before departure will go a long way in getting you to your destination. This could happen with any airline, and not all of them would issue you a $150 voucher.