How can antigenic mimicry lead to an autoimmune response?

[warya]

Notes say:

An autoimmune disorder occurs when the immune system fails to recognise its own body cells as 'self' and begins to attack its own cells and tissues
Some pathogens try to evade the immune system be producing antigens which closely resemble those of its host (antigenic mimicry)
If the pathogen is detected and destroyed, B-cells will be activated that produce antibodies specific to molecules similar to those on body tissues
This may lead to the destruction of tissues that contain those molecular fragments

But I can't quite make sense of it, are antibodies produced specific to the pathogenic antigens, which attack the pathogens but also attack 'self cells' with the same/similar shaped 'antigens'? If so, then why was the pathogen recognised as nonself anyways, seeing as it has similar antigens as self cells?

[vox nihili]

Notes say:

An autoimmune disorder occurs when the immune system fails to recognise its own body cells as 'self' and begins to attack its own cells and tissues
Some pathogens try to evade the immune system be producing antigens which closely resemble those of its host (antigenic mimicry)
If the pathogen is detected and destroyed, B-cells will be activated that produce antibodies specific to molecules similar to those on body tissues
This may lead to the destruction of tissues that contain those molecular fragments

But I can't quite make sense of it, are antibodies produced specific to the pathogenic antigens, which attack the pathogens but also attack 'self cells' with the same/similar shaped 'antigens'? If so, then why was the pathogen recognised as nonself anyways, seeing as it has similar antigens as self cells?

Not a question I'd imagined you'd get in VCE, to be honest. If so, it'd be a high level one.

Basically, if the immune system manages to launch a response against the antigens that are similar to host-cell antigens, then it may produce antibodies that are able to bind host-cell antigens (as well as those on the pathogen that are similar) and therefore kill the host cells.