You are correct. For reasons of expediency I did not mention that there's a "difficulty" factor which is usually expressed by a variable LOC/hour rate. e.g., Server backend code might be estimated at 100 LOC/day whereas code for an 8-bit embedded controller might be 10 LOC/day.

I think the idea is that, when you're measuring in units of many thousands of LOC, those differences roughly average out.

Whether that's true across widely differing parts of such a huge system I'm not convinced, but within a single more typical software project it seems believable to me.