In offline mode, cached map data is used for rendering, routing, searching, etc. So since you have downloaded the map region package of interest, viewing and routing requests related to to this region will be done with the cached data.
Please read this reference (also applicable to iOS):
https://developer.here.com/documentation/android-premium/dev_guide/topics/routing-offline.html
And as stated on the reference page:
There is no guarantee that online and offline routes will be the same as different algorithms are used for online and offline route calculation. Online route calculation is performed on high performance servers, therefore more computationally intensive algorithms are used online, which cannot be used offline. Online route calculation should be preferred and offline routes are expected to be used as backup especially when there is no connectivity.