He never heard the explosion. How would he have? The sounds were produced by the reaction of suddenly super heated air and uncountable billions of pieces of shrapnel ripping through, and shredding apart, the wood and metal warehouse, as well as the far less resilient bodies of the two flesh and blood people trapped within.
He didn't really remember waking up in his grave. Or digging out of it. More like there was a point in the pain where everything was only cramped, soundless, darkness..before giving way and then he was being smothered by cold all enveloping weight....
No, he didn't have to have clearly and distinctly perceived and registered every single pain and horror that had taken place in those events. Because his subconscious was more than willing to fill in the blanks....
"Poor little birdy, you've gone a gotten all Broken! No good for Batsy now...'"
And dredge up ancient history, for no reason other than to add to the complete suckiness of it all, while it was at it.
" Worthless little shit! I'll teach you! Cath! I told you to get me some more beer! SO GET OUT OF HERE AND GO GET ME MORE ! "
And sometimes it even added junk
" Love the new look! I'm thrilled! I'm honored! The Bats are just gonna die when they see what I've made of you! "
The echo of that laughter and his own screaming woke him. Choking on the memory of the liquid from the Lazarus Pit, on grave dirt, on his own blood.