Without looking into the code - this is not posible. NTFS supports hardlinks which are not commonly used. Two or more files can share the same content. Basically there is one file that is referenced to at different places of the file system.
A CR2 file though would have a different content than a JPG file. Therefore they would differ and occupy different locations on the disk.
Your particular result is probably due to another reasonable assumption in the code of Photorec:
Data that is assigned to a certain file won't be assigned to another file.
If Photorec's guesses fail, a failed file may contain content that belongs to another file that could have been recovered when searching for just that extension.
If Photorec acted differently, the recovery results could require a multiple of space of the failing drive/partition.
As there is so much information around on cgsecurity.org, the following beautiful page can easily be overseen.In any case, massive thanks for your work on the software.