Yes, this is wrong and he must be advised and informed that our Prophet, sal Allahu alaihi wa sallam, did not do this. Never the less, his prayer is valid and correct but he has left the sunnah of reciting it silently.

My grandfather prays Dhuhr and Asr by him self but he prays it aloud (we can hear him clearly) its like he’s praying Isha. Is it wrong or is it ok?