Resolution:
yes, byte rate can be non zero when message rate is zero.
consider the following exammple:

1. Statistical interval is set as 30 seconds in the conf file.
2. Publishing a message with the size of 1000 bytes every 10 seconds.
3. It means 3 messages will be sent over the statistical period of 30 seconds.
4. Now message rate per second is 3/30 = 0 (It is expected).
5. But if we calculate the byte rate per second,
   (Message count * Message size) / (Statistical period)
   3 * 1000 / 30 = 100
6. In this case, the byte rate is non zero though message rate is zero.