It goes far, far beyond Dockerfiles. Are you on-call for production? Can you debug a problem in production?
If not, then that's the root of the problem that the dude is talking about. If these are true for you (not specifically you, any reader of this):
- You don't have a good idea of how to ship a change all the way to production after committing it
- You would not know how to debug and fix a failure of your code in production
- Your "Dev" and "DevOps" teams are in separate departments
...then congratulations, you have just reinvented the old-school sysadmin/developer dichotomy from the 90s. You just happen to be using Dockerfiles instead of Makefiles.