Lineweights can be assigned as Layer property. You have them all "Default".
If an object has lineweight property assigned "ByLayer", then it takes lineweight from the layer in which it resides.
If an object has lineweight assigned to some value, as some of the objects in your drawing, then this value will be used to represent object's lineweight. That is why some objects in your drawing have "incorrect" lineweight.
Now about current lineweight - if it is set to "ByLayer", all newly created objects in the drawing will be created with lineweight property "ByLayer". If lineweight set to some value, for example to 1.00 mm as in your case, all newly created objects will take this (1.00 mm) lineweihgt regardless of the layer on which they are located.
Maxim