why mysql binlog creating new log file daily
4. I have no CRON which do some task auto magically

I'll speculate that you actually do.  Linux systems often use the logrotate utility to manage rotation of log files from numerous disparate subsystems.

Distro builders love to coerce software installed from packages to Do Things The One True Way™ so it should not surprise you if they have "extended" MySQL server beyond the official documentation, to rotate its own binlog.

You may find syslog entries mentioning "logrotate" around the time that the binlog changes, and further explanation is likely to be found in a file somewhere around here:

/etc/logrotate.d/mysql-server