why is the first short, poetic episode about michael holtzapfel an example of dramatic irony? who was unaware of the event at this point?

We all know that Michael can't handle the death of his brother, the guilt is just too much. Death explains that it is not the dead, but the survivors that it cannot stand to look at. Michael Holtzapfel is one such survivor who could not stand the guilt associated with having survived while his brother died.

Its ironic, because Michael killed himself because he survived, at this point nobody is unaware of this but frau Holtzpafel the mother who wil receive the news