Not the parent, but this is exactly what happens. ArgoCD is pointed to an "application" chart which just points to a path of a helm chart (of your app/sevice) in Git. So when your CI changes the image hash in the values file in your helm chart, ArgoCD with notice that, and change the deployment resource's image hash. It is just a nice system to have resources in sync between your git repo and what you have live in the cluster. Of course, if you change anything else, ArgoCD will change it too.
You're also right, rolling back just includes changing the hash back to whatever you had, or to a new hash which was a result of a git revert or whatever. Also the good thing is that if that newly deployed service is very broken (that it doesn't pass the k8s health check), ArgoCD will hold on to the old ReplicaSet and will not let your service die because of it.
What's also nice about ArgoCD is that you can play a bit with some service/application in a branch. Say you have some live service, and you want to adjust some configuration of it. Usually third party services have a lot of options to set. The problem is that you're not 100% sure how to get what you want, so doing a pull request for every small change can be very slow and exhausting. To work around that, you can point your ArgoCD's application chart to a chart which is in a branch, test/dev/fiddle with just pushing to that remote branch, and when you're satisfied, you merge your branch, and at the same time point your ArgoCD application manifest to point to the master/HEAD for that chart. In effect, at this step, only your Git repo will be updated, your service already has all the changes so ArgoCD will do nothing. That way you can iterate faster, and undo whatever regression you've introduced just by pointing ArgoCD to watch the master, not your branch (or you can just reset your branch to be indentical to master).
You're also right, rolling back just includes changing the hash back to whatever you had, or to a new hash which was a result of a git revert or whatever. Also the good thing is that if that newly deployed service is very broken (that it doesn't pass the k8s health check), ArgoCD will hold on to the old ReplicaSet and will not let your service die because of it.
What's also nice about ArgoCD is that you can play a bit with some service/application in a branch. Say you have some live service, and you want to adjust some configuration of it. Usually third party services have a lot of options to set. The problem is that you're not 100% sure how to get what you want, so doing a pull request for every small change can be very slow and exhausting. To work around that, you can point your ArgoCD's application chart to a chart which is in a branch, test/dev/fiddle with just pushing to that remote branch, and when you're satisfied, you merge your branch, and at the same time point your ArgoCD application manifest to point to the master/HEAD for that chart. In effect, at this step, only your Git repo will be updated, your service already has all the changes so ArgoCD will do nothing. That way you can iterate faster, and undo whatever regression you've introduced just by pointing ArgoCD to watch the master, not your branch (or you can just reset your branch to be indentical to master).