Conversely, I've seen code written in Java where instead of using objects the original coders used hashmaps with key/value pairs for fields. Sometimes they used some public static strings or an enumeration for the keys but often times they're just randomly hard coded throughout the program with string literals for field keys.
In another system I've worked on the coders did not understand objects/collections at all. So rather than having an array of type Person you had the Persons object that looked like this:
While it's true that good vs bad code is somewhat subjective... code like the examples I provided above is pretty horrible by the standards of all but the worst coders.
Are you sure they didn't do it for performance? That is a well-known pattern for getting better data locality ("structure of arrays" vs. "array of structures").