Proper irony is just sarcasm, which is the lowest form of wit. People act like "irony" is some magically great thing and that people "doing irony" wrong as somehow at fault. It's pretty silly. going off dictionary definitions:
noun: irony
the expression of one's meaning by using language that normally signifies the opposite, typically for humorous or emphatic effect.
Which is plain sarcasm, and not relevant in this case. However, the other two dictionary definitions are relevant:
a state of affairs or an event that seems deliberately contrary to what one expects and is often wryly amusing as a result.
"We beat Communist Japan" fits this one.
a literary technique, originally used in Greek tragedy, by which the full significance of a character's words or actions is clear to the audience or reader although unknown to the character.
I'd say it also fits with this one too. How contrary the character's words were in relation to the real situation was clear to the audience but unknown to the character.
For example, say there was a story where the main character someone killed someone they believed was a Soviet agent, yet it turns out they weren't a Soviet agent after all, and the person who helped them kill the "agent" turns out to the the real Soviet agent. That's clearly
ironic but it maps directly onto the current question.