It may be that the toad wandered in when it was a toadlet, either looking for shelter or a meal. I saw on a program, or read about it somewhere, that a mummified toad was found inside a rock that only had a tiny opening. Presumably it got too big eating whatever crawled inside and couldn't get out again.
Trying to find information on it, I came across a few examples of this, there's one in Brighton Museum mummified inside a nodule of flint.
Just read about two who were liberated, one in Aus and one in the uk, from inside stones / cracks etc and they both died within minutes of freedom
