Hanabata,

Just what is, in your "strict sense" a fire door?  By definition a fire door IS a fire resistant door constructed to a certain standard.  Unless you have in mind an infinitely fire-impervious door (that doesn't exist) akin to a "bulletproof" vest, I fail to understand your confusion.  Actual standards for fire doors vary but it would not surprise me that even a building constructed in the 1970s incorporated fire resistant doors in its specifications.

If you remain confused, I suppose you could look up the original contractor's specifications for the Marco Polo.  Or, failing that, you could take a moment to google what the definition of a "fire door" is.