Comma vs Semi Colon

[AJJ837]

According the SC Strategy Guide, the dash in the sentence below could have been a comma instead, and the sentence would still be correct. My understanding is that you can only use commas when dealing with 2 independent clauses if the clauses are joined by one of the FANBOYS. In the sentence below they are joined by "although", which is not a FANBOY, so I am wondering why a comma can be used here? I thought a semi-colon would have been more appropriate but seems I am wrong. Thanks a lot

By January 2, 2000, the so-called "Y2K problem" was already widely considered a joke -- although the reason for the non-event was the prior corporate and governmental investment in countermeasures.

[Sage Pearce-Higgins]

There are other words apart from FANBOYS that can join together two independent clauses. These include if, because, when, until, although, etc. You can test this by making up some simple sentences.