That's some bullshit. you did the right thing. When a new employee joins and notices that something sucks the answer should be something like these:

We know, but haven't had time to fix it, maybe we'll assign that to you when you're caught up.

We didn't think of it that way, good catch, lets go into detail later.

Yeah, but doing it this way makes this other thing easier, we'll show you that when you're ready.

or even: I don't know, my brain is fried with this project, can you ask again in a few months?