Al-Masudi was a very able cartographer, and his 10th Century map of the world is really impressive. And yes, it includes a continent to the West of the Old World.
Obviously this doesn’t prove a genuine knowledge or discovery of the New World, but its a noted oddity.
The theory that a Muslim population discovered and settled in the Americas is widely discredited and shouldn’t been taken seriously, but it is a published theory and supported by at least some academics. Most though dismiss is as either ‘psuedo-history’ or even ‘propaganda’, so yeah…
This theory might be ahistorical, but how sinister it is is debatable (“Yeagley believed that Shabbas and the other authors were simply trying to gain acceptance for Arabs, further integrating them into American culture by making them ‘native.’”). The American myth making around Colombus might be more based in fact, but lets be honest, there’s a lot of fake history there too.
The word ‘admiral’ does come from the Arabic ‘amir’, - circuitously via medieval Latin and Old French.
So yeah the post is untrue, but I wouldn’t call it ‘insane’ necessarily. Its a reasonably common, and interesting, myth.