Interesting question. I'm Korean and actually I was asking myself if "codes" is correct English while typing. I don't know, but except for grammar "code" seems to be countable to me.
Note that Korean grammar (and maybe some other languages) doesn't have strict rules about plural forms.
Anyway "Codes" make sense to me when they refer "snippets".
Yes, I think it's something some American developers have picked up from others using "global" English. I heard the plural used a lot from devs in and from the Indian subcontinent, and now, I'm starting to hear native American devs use the plural form.
Note that Korean grammar (and maybe some other languages) doesn't have strict rules about plural forms.
Anyway "Codes" make sense to me when they refer "snippets".
edit: added some more thoughts.