Pytest and mixer does not raise errors when testing non model fields

Question

I am following Test driven development and am working through Django models with mixer, Pytest and pytest-django.

This is the test for the Project model:

class TestProject:
    def test_model_valid_fields(self, django_user_model):
        project = mixer.blend(
            'workspaces.Project',
            title="Road map",
            non_model_field="some value"
        )

        assert project.pk == 1
        assert project.title == "Road map"
        assert project.non_model_field == "some value"

The Project model, notice that Project model has only the title field:

class Project(models.Model):
    title = models.CharField(max_length=200)

Two things:

1. How is mixer allowing the use of non model fields?
2. Why is Pytest not raising an error, since the Project model does not have non_model_field field?

What am I missing here?