There are several types of locks available for moderator use:
- Content dispute
- Historical significance
- Offtopic comments
#2 - Historical - is special: when applied to a question it also locks all answers. But #1 and #3 only apply to the locked post itself: locking a question doesn't prevent the answers from being edited, voted on, or commented on.
The Android app doesn't appear to respect this distinction however, at least when it comes to comments:
Even though this answer isn't locked, the banner still shows - and no comment input is possible.