That is incorrect... 400 feet from obstacle vertically and horizontally... If you are inspecting a 600 foot tower, you can fly up to 1000 feet up and 400 foot from side... (like a 400 foot bubble) You do however need to adhere to other airspace requirements that might be in place...
Edited to say:
That area of Chicago is advisory zone due to hospitals and helicopter traffic... "Fly with caution..."
First off, OP, that was some very nice footage.
Now, to the quoted text. This info is partially accurate.
1. If you are not part 107 certified, your ceiling is 400’ AGL Unless it is lower in restricted airspace.
2. If you are part 107 certified:
A. If you are in class B, C, D or E2 airspace, 400 AGL is the limit and it may be lower in certain airspace, generally around airports. If you need to go higher, you must get a waiver, if you can. It’s going to take a very good reason to get one.
B. If you are in class G or E (except E2) airspace, the 400’ around and over an obstacle is accurate.
The OP was under ORD’s class B airspace in class G to 699’ AGL, them Class E with the 700’ floor. There are advisory zones where he was flying, but if the underlying activities were not going on, this flight would not have required a waiver.
