I consider blasphemy to be a category of "moral injury". It's an offense against a societies morality/beliefs that is similar to a racist or sexist statement, or walking around with sperm on your face (but I don't think any of them should be illegal) At it's heart, religion isn't much more than a way to enforce specific morals/beliefs on large groups of people. If you believe God thinks you shouldn't do something than you believe doing that thing is immoral.

I'd say your initial comment is essentially the same as saying "that's not a dog it's a Labrador".