How?
They could expose the issue without the 90 day grace period if they wanted to be dirty.
How? Because they have appointed themselves as an authority over their competitors and decided to take it upon themselves to publicly expose their problems. That's being not only dirty, it's acting like a ********. I don't respect people that tell others "you fix what I found by the time I say or I'm going public with this." Who made Google the arbiter? Who made them the police of security? What makes them think that they are special enough to start exposing possibly unknown exploits in their competitors businesses? How is Google making themselves in charge of what gets exposed their perogative? Google is doing nothing more than making themselves look good. You can guarantee that if people started tearing apart Android looking for bugs they'd not speak of them (like they already do), they would never admit there were serious bugs in it (like they already don't), and you can bet your ass they'd go the first media outlet that wanted to talk to them and start saying how their competitors were trying to badmouth them, ruin their name and probably talk about legal action. Google is not doing this for the greater good, they are doing this to make their competitors look bad.