Note - I don't have many reference devices, so far this is only occurring on my Nexus 4 with Android 5.1.1
Steps:
Download an article pack from http://download.kiwix.org/zim/wikipedia/
Navigate to offline articles
Tap the article pack
Expected Result:
On the new device it looks fine:
Actual result:
Looks like a poor quality image
@Nicholas.tsg - Can you please try this on a couple of your older android devices and see if you can reproduce it. Let me know if you need help finding a content pack