I'm not knowledgeable but my guess would be the sending network had passed on your text to the next network in the line, so sent you a 'sent confirmation'. The recipient didn't get the text so somewhere along the line it got lost. I don't think these texts are guaranteed delivery.
It was my understanding that the sending network will keep a text for a limited amount of time so it can retry if it gets a failure message returned, but it seems it believed your text had gone, given the confirmation you received, so my guess is that its saved copy would then be deleted.
As for all the other networks on route, I'd not like to say. I suspect they don't store them, but just make 'best effort' at delivery.