Google is happy to strengthen another Android OEM to balance out the ecosystem, keeping Samsung from dominating. They focus on the software which is their strength. I'm curious whether they have some clause to keep Lenovo from dropping Android in the next x years.
Sounds like a bad deal at first, but considering this and looking at the numbers it's a good move for both companies.
Even without the clause I doubt Lenovo would choose to drop Android. With the Moto X/G, Motorola has strong momentum as an Android handset manufacturer. This includes consumer expectations that it will continue to make Android devices. Since Lenovo has no desire to (and is too late to) start a forked Android ecosystem a la Amazon/other Chinese manufacturers, sticking with Android makes the most logical sense.
Sounds like a bad deal at first, but considering this and looking at the numbers it's a good move for both companies.