"Codes" as a way to refer to programs/libraries is actually common usage in academia and scientific programming, even by native English speakers. I believe, but am not sure, that it may just be relatively old jargon, before the use of "programs" became more common in the industry.

As for the grammar rule, it's the question of whether a word is countable or uncountable. In common industry usage, "code" is an uncountable noun, just like "flour" in cooking (you say 2 lines of code, 1 pound of flour).

It's actually pretty common for the same word to have both countable and uncountable versions, with different, though related, meanings. Typically the uncountable version is used with a measure of quantity, while the countable version denotes different kinds (flours - different types of flour; peoples - different groups of people).