Has anyone confirmed it's a case of Swyer syndrome?

No and that's part of the issue related to the whole discussion. Lot's of conjecture, not a lot of detail. If you look at the IBA statement which you shared (thanks for that btw), it says the following:

"Point to note, the athletes did not undergo a testosterone examination but were subject to a separate and recognized test, whereby the specifics remain confidential. This test conclusively indicated that both athletes did not meet the required necessary eligibility criteria and were found to have competitive advantages over other female competitors."

They didn't say why the athletes failed eligibility, other than they used recognized testing that it wasn't testosterone examination. That statement leads me to believe it was a chromosome test and that Sywer syndrome seems like the most likely explanation. But ya, that's conjecture, not fact.