This is a printing error where the cover art intended for issue #52 was mistakenly used for issue #51. Diamond's previewsworld.com site originally had the incorrect cover (it was replaced) hence
they, as well as the printers, also appear to have been sent the wrong art for the cover.
There are two error variants, the Newsstand (bookshop) edition, priced at $4.99, and the Direct edition, priced at $3.99:
The barcodes also differ between the Newsstand (bookshop) and Direct editions, with the Direct editions marked as "Direct Sales" in the UPC:
The cover for #51 was corrected (both Direct and Newsstand) and this is shown below alongside the cover for #52, which also has the title "Meet The New Man Of Steel...".
Interestingly, one seller on ebay claimed that the replacement #51 $4.99 Newsstand variant is hard to find.
It is not known exactly how many copies of each of the error variants made it to the public but there seems to be a lot more Newstand (bookshop) variants available. Anecdotally there were reports that only a
very few cases of the Direct edition made it out for orders placed within a space of a few specific dates.
As of November 6th, 2016, the CGC grading census recorded:
12 Direct editions ($3.99) with the correct cover.
40 Direct editions ($3.99) with the incorrect cover.
01 Newsstand editions ($4.99) with the correct cover.
45 Newsstand editions ($4.99) with the incorrect cover.