It's not just two programs reporting the same value. It's SSD controller reporting TBW amout that grow exactly as fast as specific kernel process writes grow in

It's not just two programs reporting the same value. It's SSD controller reporting TBW amout that grow exactly as fast as specific kernel process writes grow in Activity monitor. smartctl just reporting information that SSD controller returns from it's own SMART data. So this data even stored independently from an operation system. Activity Monitor on other hand actually watch all system IO of currently running processes and keep record of how much each process writes / reads from / to disk while being monitored.