Avast shields,in your case it was network shield, just saved your computer from being infected,you will get that page you showed in screenshot only when you click more details.
The Main moto of avast shields is to prevent you from getting infected and it does that by aborting the connection and blocking the infection right away when its a case of web based attack and then the infection cant touch your machine
If you right click on the avast ball in your tray and hit show last pop up message you can re-review the last popup alert from avast.