"Eurovision is first and foremost a celebration of European spirit, of our European diversity and talent. The EU flag is a symbol of this," Schinas said on X on Saturday evening.
"Less than a month to the European elections, there should be no obstacles, big or small, to celebrating what unites all Europeans."
Not all participants are in the EU. Strictly-speaking, you can maybe argue that the identical flag also applies to most non-EU members as the Flag of Europe, given that pretty much everyone is in the Council of Europe, but it probably still won't cover Australia.
That being said, I mean, I don't really see the problem of someone holding the EU flag if they can hold their national flag. I mean, a flag doesn't have to apply to everyone.
Besides, the thing is "Eurovision" already, not "Euroaustraliovision". If you want the venue to be some sort of generic thing decoupled from Europe, you've already done the branding wrong in rather more-significant ways.