files deleted with no record?

I just encountered a situation where a merge was made, with no apparent changes in files (ie no log), but the result was that some files were deleted.

person A adds some files person B adds some files from the same point person B commits and pushes. person A commits -- now merge is required a few more commits on top of person B's commit person A merges - this removes the files that B added. There is no log of the files being deleted

Clearly this is possible - was this a user error?

Thanks