Disney Canon
There's actually very little in this canon linking them to Mandalore other than their armor. In fact, as of right now, the only thing establishing them as being Mandalorian is the card back for Jango's figure from the Star Wars: Rebels toy line.
The ruthless Mandaloria warrior and resourceful bounty hunter Jango Fett fights the Jedi on the planet Geonosis.
The disconnection is largely an artifact of the canon purge.
Previous EU Canon
This is where the Mandalorian connection was originally established and fleshed out.
The comic series Jango Fett: Open Seasons establishes that Fett was born and raised in the Mandalorian sector.
While Boba Fett was not born or raised there, he would later join the Mandalorian Clan and become their leader, The Mandalore, allowing him to call himself a "Mandalorian".