Why does my iPhone 6 do this?

Look on the bottom left hand corner of the screen shot, it has a little picture of the app icon I have for Schoology. I deleted the Schoology app but then it had a little icon of the App Store icon. I don't know it's doing this! And the weird thing is it only does that when I'm at schoo O_o Anyone know what's up?Why does my iPhone 6 do this

Those are called "Lockscreen shortcuts".

http://www.cultofmac.com/296302/hidden-ios-8-features/

They change based on your location.