Well, maybe they should not have given away how to easily fake a screenshot yourself, but still some useful tips to keep in mind. It helps to know what to zoom in on to look at.
I did not know about the Forensically app, which is a web based app that can analyse any image in depth and create heatmaps of stuff that’s been edited in.
See https://www.howtogeek.com/how-to-check-if-a-screenshot-has-been-photoshopped