Good for Nathan. I didn't realize he'd be a graduate transfer. Nothing odd about it, graduate transfers happen all the time where kids go somewhere to pursue their masters. We get them too.
About being 3rd or 4th string in the fall, we knew about his knee. It's equally plausible that he tried to give it a go and get some reps, but that he and coaches realized it was too soon and he needed to rehab. The last thing you want is a kid rushed back and go down to make it worse. And if that had happened, the coaches would've really been skewered, and rightfully so.
As far as Sumlin not mentioning him, Sumlin doesn't talk about injuries. And if he did, what would he say? How many times would you want him to say, "He's hurt." Or be listed on an injury report, which we don't have anymore, as "Out for the season." Coaches don't typically say much about a kid is who is out for the season, which Eldridge obviously was. And because of that, it's speculation and not a fact that "the coaches didn't fully embrace him."
Sorry, but my take on this speculation that there "has to be more" is: Maybe, but there doesn't have to be more than he was out for the season rehabbing an injury and is now a graduate transfer.