It probably dates from the 1970s when a building in the centre of the city was abandoned. Not the prettiest building, but it will be demolished to make way for houses and a new fire station. See here for an artist impression: www.unity.nu/Artikelen/leiden/eerste-beelden-nieuwbouw-brandweerkazerne-en-appartementen-beschikbaar
sleutelstad.nl/2018/03/07/woningbouw-en-brandweerkazerne-op-plek-oude-postkantoor-schipholweg

Two stone lions from the old post office were put on this building, they are in the wooden casing for protection.