I am learning Chinese, and have noticed a number of Chinese people referring to all elevated rail as "qing gui" for "light rail", even for heavy rail lines such as the Chicago L. Is there another term, or is this a habitual thing?

Yes, this is a frequent mis-labeling. A lot of Chinese believe urban rail is somewhat "lighter" than "railroad" rail.

Most Chinese urban rail lines are heavey rail (zhòng gŭi).

Qīng gŭi also became a kind of colloquial reference to all-elevated lines. So it is not strange that Chinese call L "light rail".

elevated rail=高架轨道
light rail=轻轨
heavy rail=重轨
cable rail=索轨
narrow-gage=窄轨
single track=单轨

what else do you want to know?

轻轨在中国一般指: 地铁+高架铁路 总和，是一个总的概念。

There are a lot of elevated national railroads in urban area, which will never be dubbed as qīng gŭi. Nor will subway.

I've read some articles in the past that described suburban rail systems like the Paris RER as "qing gui". Perhaps because rail urban transit is still new to China, it will take a while for all the technologies to sink into the minds of people.

elevated rail=高架轨道
light rail=轻轨
heavy rail=重轨
cable rail=索轨
narrow-gage=窄轨
single track=单轨


elevated rail=高铁
light rail=轻轨
monorail=单轨

Monorail of Chongqing is also called 轻轨,as few Chongqingers know the fact that it's actually a monorail,not a light rail.

And Shanghai's elevated metro lines are also labelled as light rail, despite being the exact same type as the ones going underground.
Really weird.

elevated rail=高铁
light rail=轻轨
monorail=单轨

Monorail of Chongqing is also called 轻轨,as few Chongqingers know the fact that it's actually a monorail,not a light rail.

高铁=高速铁路=HSR

And Shanghai's elevated metro lines are also labelled as light rail, despite being the exact same type as the ones going underground.
Really weird.

Not really, aren't lines 5 and 6 of a much narrower, smaller car type than the rest of the system (except line 8 but that is an anomaly in my opinion)? They also only have four cars per train. So I guess its pretty appropriate to call those "light rail". But yeah Line 3 and 4 with their 23m long, 3m wide trains are certainly not light rail but heavy rail.

What do people call Shanghai Metro Line 4? Is it "di tie" when underground and "qing gui" when above? Pardon me, I can read Chinese on this computer, just cannot type it.