You can make fun of the language but it's not as though firewall has always referred to the software on a computer system to restrict network access.
From a quick Wikipedia search:
The term firewall originally referred to a wall intended to confine a fire within a line of adjacent buildings. Later uses refer to similar structures, such as the metal sheet separating the engine compartment of a vehicle or aircraft from the passenger compartment.
The computer use of the word was a metaphor for the physical thing and the MP's usage of the word is too just with a different meaning.