While I am not sure that you could tell if text was cropped through that app, without seeing the original message (as in you were both sent a larger message, but then the person forwarded you only part of the message, so you could see they had cropped it). However I do know that you can create fake messages on that app.
There is a way you can prank your friends WhatsApp by using WhatSaid.
You would be able to create a fake conversation with anyone by adding their pics, giving them the persons name, and creating your own messages (for both you and the "faked" person).