Is this type of San Diego Airbnb illegal?

[Brian Mihaljevich]

Hello BP San Diego! My name is Brian and I'm an active duty Marine Corps Officer. I'll be stationed in SD for 4 years beginning in Jan 2020. I'd like to buy a 3 bed, 2 bath property with enough yard space to add an ADU and rent it out on Airbnb. This seems slightly easier than finding a multi-family property plus my fiance is excited about making the ADU Instragam-worthy.

Here’s my question: is it illegal to rent out ADUs on Airbnb? The last bullet of the San Diego County Zoning Guidance document (Link) appears to state that this type of Airbnb listing is not permitted. A quick search on Airbnb shows many guest/back house available to stay in. Are all of these Airbnb hosts simply breaking the law or am I missing something?