Statistics Summary Output to Stderr, why?

First, fantastic utility, it has come in great handy!

I've been invoking hping in a context, where I do two things:
capture both the Stdout where each packet result is logged
and
capture statistics of the entire set of packets.

I noticed hping's statistics are piped to stderr, and for a point of comparison I checked that Mac OS X's `ping` logs the summary at the end of Stdout.
So I became curious, whether there's a specific design motivation for logging statistics on Stderr rather than at the end of Stdout? :)

https://github.com/antirez/hping/blob/master/statistics.c#L32-L39