Dead Bearded Dragon Rescue, Trying to See What Happened

[Armiyana]

I also have to be skeptical about the yellow fungus. While it DOES happen, this beardie looks to have an all over bright yellow coloration that isn't due to a disease, though I do notice a few open wounds around one side of the face? Was he previously housed with other beardies before rescue? Also, how long was he in your roomie's care? What was his diet like before and now?

It's hard to say what happened. Especially with no other symptoms. The bulging eyes, closed nostrils, dark beard and sand does make me think he choked somehow.

I do agree with Hugsplox to an extent, it's a huge debate. I tend to side on the 'no' sand side myself. By that I do something similar and have a slight dusting of sand over a tile or slate rock base or a small dig area. For my leopard geckos I personally used dry coco husk in a dig box because they don't like the taste if they get a mouthful.
Without seeing a clear belly or back picture, it's hard to get an idea of how 'healthy' the beardie looked otherwise... The head/beard almost looks more streamlined like a female's to me. Are you sure it was a male? Because eggbinding could be a cause in that case as well... If he had never been housed on sand previously and switched to sand, he could have eaten quite a bit when you weren't looking as well. If he had been calcium deficient in the prior owner's care, some beardies will devour sand in an attempt to build up calcium. (regardless of calci-sand vs other sand types)

The bulging eyes.... can actually be normal to an extent in beardies. So that is also a bit of a headscratcher. Beardies will bulge eyes when getting ready to shed, some people think that it's also like a 'yawn' in humans...so I wonder if he was unable to breathe if that was a side effect with the yawning theory. Some birds will yawn excessively when they have URIs and can't breathe well. It can also be a sign of vitamin deficiency though...and that could be something as simple as the bulb having expired. UV bulbs will still give light, but the actual UV effects lessen over time so they can be checked with a UV reader card or just change them out every 9-12 months as a precaution. If the previous owner hadn't been properly supplementing diet and changing out bulbs, that could be a reason for the bulge but I don't see it as a sudden cause of death unless it was EXTREME and you would see other signs like metabolic disease as well.

And the last thing that I can really think of offhand is possible organ failure. If the previous owner had him on a diet of insects only and not giving enough veggies to his diet as well, there could be a buildup of protein that can cause organ failure in beardies. Something that again falls to previous ownership more than the care that you gave.

Regardless, I'm really sorry for the stress and sadness that this is causing. Rescues can go downhill so quickly sometimes, even when we try to do everything right.