How is Android allowed to use the name "Oreo"?

Google paid nothing, but has a "pure co-branding partnership" with the owner of the trademark, Mondelēz, according to this article.

Google did not pay the famous cookie's maker, Mondelēz, any money to
use the name, said spokeswoman Valerie Moens, who in an email called
it a "pure co-branding partnership." The company said in a news
release, however, that it and Google will partner on a "variety of
global initiatives designed to create innovative, playful experiences
for both OREO and Android fans." These, Moens said, will include a
drone flight that projects a holographic version of the Android and
Oreo superhero, some Android and Oreo-branded cookie giveaways, and
four short films featuring the new character.

So in this case, allowing Google to use the name "Oreo" is seen as beneficial to both organizations and will be used for inter-company marketing.