I somewhat agree with the EU here. It's far too generic, "Open" and "AI." To grant the trademark would mean any AI product that actually IS open, or open source, etc. cannot say they are "Open AI" which IMO would be a problem.
Where I might disagree with the ruling is spacing vs. no spacing. I'd have granted them the trademark on specifically "openai" as a single word but not "Open AI". Let's them defend their name against anyone else calling themselves "OpenAI" but not any other product advertising itself as "Open" "AI".
Entirely possible, seeming more likely, that I didn't have enough background information on the short article.