The figures are nonsense, theres no way to measure the number of people who chew in proportion to the very large population especially if actuall data hasnt been done compiled by the local government or an international agency. Perhaps the mention was alluding to the precense of qaad in the city.
Bosaaso is a melting pot from Somalis all over the country, the large number of Khat is easily explained by the large Isaaq population.
Secondly Khat is used far less and hardly known known in cities such as Garowe, Qardho, Galkacyo, where Somalis specifically native to the region inhabit.
This drug is especially notorious with Isaaqs who have introduced it to Somalia.