# Confused with mesh analysis

something about mesh analysis confuses me and I can't find an explainaton anywhere, as you can see on this picture (it's in French, but the schema and formulas should be enough to understand)

They bascially explain how mesh analysis works, and that's fine and all, I understand the formulas but then I get this exercise :

And as you can see they just put I2 = -2A. Why do we not care about the 12 and 3 resistances ? The exercise is basically the same as the image shown above and in that one we take both R2 and R3 into account.

Is it because this time we have a current source ? Or because we are on the "edge" on the circuit ?