On a debian buster i added the repo

deb     http://deb.kamailio.org/kamailio51 buster main
deb-src http://deb.kamailio.org/kamailio51 buster main

But when i install i get 5.2, is this right?

additional info:

# apt-cache showpkg kamailio
Package: kamailio
Versions:
5.2.1-1 (/var/lib/apt/lists/deb.debian.org_debian_dists_buster_main_binary-i386_Packages) (/var/lib/dpkg/status)
 Description Language:
                 File: /var/lib/apt/lists/deb.debian.org_debian_dists_buster_main_binary-i386_Packages
                  MD5: df3e15f422439e08c305782f5650a98c
 Description Language: en
                 File: /var/lib/apt/lists/deb.debian.org_debian_dists_buster_main_i18n_Translation-en
                  MD5: df3e15f422439e08c305782f5650a98c

5.1.10.1+bpo10 (/var/lib/apt/lists/deb.kamailio.org_kamailio51_dists_buster_main_binary-i386_Packages)
 Description Language:
                 File: /var/lib/apt/lists/deb.kamailio.org_kamailio51_dists_buster_main_binary-i386_Packages
                  MD5: ebddf40d0dfbfde1c479419970f978c7