If Roku didn't pop the app icon on your screen, you likely would never have known about it. So how would you know to install it and check it out?
If you read the terms of service that you acknowledged when you signed up for Roku (you have read it, right?) you'll see that you have given Roku permission to add or remove apps from your device without your knowledge or consent. Usually they are only removed if the provider terminates their agreement with Roku, or they are violating their agreement (usually offering content without legal permission). But on occasion they add a new app (such as Howdy) simply to make people aware of it. Don't like it? Just remove it and go on your way.
New? Roku has done this from the beginning. This is nothing new.