So is Wiki, apparently.
“The earliest known documents written in Swahili are letters written in Kilwa in 1711, in the Arabic alphabet.”
http://en.wikipedia.org/wiki/Swahili_language
It’s not unheard of to write Swahili in Arabic letters. In fact, the word Swahili comes from the plural of the Arabic word “Sahel” = coast and the plural is “Swahil” = coasts.
Now, the noun that doubles up as an adjective is the Arabic word “Swahili” = coastal or a male who lives on or near a coast.
Swahili language is derived from Arabic to start with.
I hope this helps.
The Arabic characters in the photoshopped sign read left to right. And the letters are unconnected, which is pretty much the only way to write Arabic left to right.
Nothing you posted changes that fact.
The sign was a joke. Arabic was used to allow for hidden messages. Swahili would not have provided cover because...it uses English characters.
Hope that helps.