It’s a language issue. We say 10 because we don’t have a single digit symbol to represent 10. If a alien with 20 fingers came we wouldn’t recognized their symbols for anything bigger than 9. Base 4 creatures don’t use 4 because after 3 comes 10 for them.
Considering this, for us humans base-10 is base-X
For the four fingered aliens base-10 is base-4. But they don’t call it base 4 because they don’t use 4 like we don’t use X. They say base-10 because for their language it’s how they say 4. And that applies for all bases.