The 24-year-old joined the north London club for a club record fee of €50 million, and Low simply cannot understand why los Blancos chose to get rid of him.
"For me, it is a bit incomprehensible that Real Madrid would get rid of one of their best players, who is of a high quality and looked more decisive than ever last season," Low told reporters.
"Mesut still needs to feel as though he has complete confidence from his coach.
"From what I heard from Madrid ahead of the transfer, you could feel that the trust was no longer there 100 per cent. Arsenal tried hard to sign him. That did him good.
"Ozil's Arsenal move will be a good transfer for the national team because he will play for a team which has an overall great technique - that is good for him."
Ozil moved to the Santiago Bernabeu from Werder Bremen in 2010, having impressed hugely at the World Cup in South Africa that summer.
The attacking midfielder went on to make 159 appearances for the club, scoring 27 times.