Exactly! I mentioned this possibility a long time ago. Also, I actually had an email discussion with Joe Zias back in 2005 concerning how he was able to say that this nailed heel bone was from a crucified man and not from some other brutal treatment. His response was:
One of the things that one must remember in our case that this period was a period of tremendous turmoil, people were being crucified left and right, I wish that the other heel bone would have been better preserved however it wasn't...
In my response to him, I posed the question again in a different way, obviously skeptical. People have accepted his theory about this nailed heel bone as the gospel, after all, and I just don't see it that way. Here's the exchange; my question is in the normal font and his response is in bold, just the way he wrote back:
However, the larger question in my mind is, given that there is only a heelbone with a nail through it, and given the wholesale brutality of those times, can we state with any certainty that this is even a crucifixion victim? Much of what we deal with in arch. is in the realm of inferences, the evidence suggests... absolute truth lasts but 20 yrs anyway.
So with all due respect, it's just a guess that this nailed heel bone might have something to do with a crucifixion and not something we can rely on as certain fact. The business about wooden pieces under the nail heads is just part of that.