Hello, I am a pc player but I was invited to the XBOX test, also in the insider program settings I have only the pc option selected.
And part of the problem is that it is the second time that happens, in the July test exactly the same thing happened to me and I did not have any solution from 343.
Please disregard the spoiler text - for the moment there is no way to swap invites mid-flight
If you were 100% not opted in to Xbox and your profile was set that way by the 13th of this month, please submit a support ticket on the Insider Support site. For situations like this you may be able to have your invite swapped over
Same problem here 