The ABC would dimly consider the presentation of homebrewed beer with commercial imagery and no labelling as homebrew as a fraudulent activity rife with consumer liability issues. Additionally, the donation of the beer until Jan 1 of this year would have been prohibited. Taxation, licensing, etc.. all the stuff that makes a regulatory agency a regulatory agency.
Had an enforcement agent come across such a presentation, they would have probably shut down that part of service and fined the licensee (severely for allowing unlicensed alcohol to be served) and had a severe talking with the server for pouring unlicensed alcohol. Additionally, future fests for the licensee would be in question due to the violation.
It's important enough to them that in AB-2609 it's stated that there must be signage at the fest entrance that homebrew is unregulated, potentially hazardous, etc. Additionally, homebrew itself must be labelled clearly that way. Even better, if a fest has both commercial and homebrewed beer then homebrew has to be physically separated with a barricade and physical monitoring and additional signage from any commercial beer.
The ABC has legal authority on how homebrew is presented and labelled and offered to the public since they regulate all alcohol in the state including defining what the boundaries are of the exemption granted by law to homebrewing. Hence their ruling on shop educational sessions. (And I know, several shops have been visited by ABC agents to have that "good" word delivered to them)
Part of why I'm spreading the word about this bill and what's allowed is that we need to have everyone on the same page and best behavior to diffuse arguments about homebrewing as a refuge for scofflaws and scoundrels for when we tackle the next parts. Incidentally, this view in nothing new - back in the 70's when the homebrewing legalization bill was written, there was a competing bill, the Conable Bill, that would have required homebrewers to register with the ATF, because the agency was worried that homebrewing would be used as a legal cover for moonshining.