Here's the source the assertion is based on: Shillington, Kevin (2005). Encyclopedia of African History. New York: Taylor & Francis. ISBN 1-57958-453-5.
This is from that source: It seems "Half Million Cairo's" Egypt lost population in beginning of 15th century because of plague:
The phrase “Black Death” was not used in the me-
dieval Islamic world. In the Mamluk sources, the dev-
astating and recurring pandemics were usually referred
to by the common Arabic nouns ta’un (plague) or
waba’ (pestilence). From the initial outbreak of
1347-1349 to the end of the Mamluk Sultanate in
1517, there were approximately twenty major epi-
demics that affected large areas of Mamluk Egypt, oc-
curring about every eight to nine years. Mamluk Syria
seemed to be slightly less afflicted, with only eighteen
epidemics over the same period. Given the descrip-
tions of symptoms and the general mortality reported,
it seems clear that the disease was that linked to the
plague bacilli Pasteurella pestis or an earlier variant
thereof. Buboes, for example, were frequently referred
to as “cucumbers” ( khiyar ) in the sources. Michael
Dols has argued convincingly that during several of the
outbreaks a total of three forms of the disease — the
pneumonic, bubonic, and septicaemic — struck simul-
taneously.
The outbreak of 1429-1430, for example,
was especially severe and was called in some sources
the “great extinction.” The accompanying epizootics
among animals frequently mentioned suggests a vari-
ant form, or perhaps an accompanying and as yet un-
determined agent.
While demography for this period is inexact, it
seems probable that the population of Egypt suffered a
prolonged and aggregate decline of approximately
one-third or so by the beginning of the fifteenth century.
Egypt’s population remained at levels lower than its
pre-plague years into the Ottoman period. The plague
did not afflict all segments of society equally. Reflect-
ing the bias of the sources, we know more about the
impact on the cities of Egypt then we do on the rural
areas. It is common to encounter statements like the
following in the chronicles: “the plague caused death
among the Mamluks, children, black slaves, slave-
girls, and foreigners” (Ayalon, p.70). The evidence
suggests that the Royal Mamluks were especially hard
hit, perhaps due to their recent arrival in Egypt, and
previous lack of exposure to the plague.
That assertion is plain erroneous. At its height, in the 14th and early 15th centuries, Cairo was a metropolis of an importance unrivaled west of China. What it does not have compared to Jerusalem, Damascus or Baghdad is a long period of historical and/or religious significance (that honor belongs to the predecessing Memphis), but that does not make it any less the richest city west of China at the time of game start, and that justifies it having the highest development of the mediterranean basin.
Cairo was never the biggest citty in west of China. Never. Who is saying that bullshit?
