Lenovo mentions that the "upgrade is only applied to the models above bought from retail market", so if you've purchased an "operator customized" or a "contract model", you might not be eligible for the update - or at least not in Q2.
As you may have noticed, the new P90 and Vibe X2 Pro aren't on the list. We assume that this is because Lenovo will launch them with Android Lollipop out of the box anyway (the P90 is expected to be released this month, while the Vibe X2 Pro should be available starting April). But we'll see what happens.
Lenovo's list of smartphones that are upgradeable to Android 5.0 Lollipop
source: Lenovo via XDA Developers