Actually, your information was still there, and most (or even all) of it was probably left intact. When you "delete" a file within the operating system, all you're really doing is deallocating that space on the platter (i.e. telling the drive and the rest of the system that the space is "free" for use). The actual data will remain there until overwritten.
In the future, it would be best to reformat the entire drive and perform at least a zero pass overwrite (i.e. deallocate the space and then overwrite every sector on the drive with a string of zeros) when transferring control/ownership of a drive to somebody else.