Ubuntu's rsync is samba rsync. It's not part of the samba project per se, but it is made by the same guy and the official url is https://rsync.samba.org/ so it's entirely fair to call it samba rsync in my opinion.

it's tridge rsync; samba is another project by the same guy. (rsync was originally a PhD thesis...)

tridge is mighty in the Linux world, he arguably greatly contributed to Linux as a server (via Samba to save on windows NT client user licenses), rsync, and IIRC reverse-engineering the bitlocker protocol thereby starting the gitstorm.

samba is different topic