We all descended from Earth yes, but in Eve that planet is all but forgotten & merely a myth used to justify weird stuff (the ‘Aliens did it!’ variant of EvE really)
Caldari & Gallente are both.
They’re a faction as in: Caldari State & Gallente Federation, usually shortened to Caldari and Gallente or State and Federation(the nations)
They’re also a race, as they both came from different worlds. Caldari were shaped on Caldari prime, a frozen iceball where resources are scarce. Add ing to this, the Caldari race is a bit more complex, as both Civire & Deteis are of Caldari descent, so you can argue that in this case, Civire & Deteis are not really bloodlines but rather factions within the Caldari Race (because, to be Civire or Deteis, you have to have an ancestry leading to Caldari Prime)
Gallente on the other hand were shaped by the lush & bountiful environment of Gallente Prime, having formed a global union by the time they went space-faring.
So yea, it can get very complex.
The short gist is, if you speak of Caldari & Gallente as faction, it refers to the State (Includes Achura too! + the large group of Matari immigrants)) & the Federation (includes Mannar, Jin-Mei, Intaki & more).
If you refer to them as race, you speak of the people that originate from Caldari prime (Not Achura & not immigrants) & Gallente Prime (Not Mannar, Jin-Mei, Intaki & others).
In short, due to the race & factions bearing the same name, it can get confusing, but they are different entities. We can go deeper, but above is a short summary & by no means complete, but should help you on the way to memorize what Caldari & Gallente & others are as race/faction.