Nokia launched the budget phone with Nokia 3 in 2017 which was running on Android 7.0 has finally received the Android 8.1 Oreo after a long time. Earlier the device had received the OTA update which pushed to Android 8.0.
As per the source, the new update is being pushed in batches and might take more time to hit the update to your Nokia 3. With major devices under Nokia getting the Android 9 Pie update seems like the company has forgotten to push the update to the Nokia 3. Anyway, Nokia has earlier promised that all of the devices launched will get the Android 9 Pie update.
The new update also brings the latest December 2018 security patch along with certain bug fixes. Probably the reason behind slower update for Nokia 3 is due to the fact that it comes with MediaTek chipset which makes the device slower with every new update.