It's important to distinguish between "chili powder" as a spice blend and "ground chiles" which are purely ground dried chili peppers. Here's a breakdown:
Ground Chiles:

This refers to simply dried chili peppers that have been ground into a powder.
It's a single-ingredient product.
Examples include ground ancho chiles, ground cayenne pepper, or chipotle powder.
These powders offer the pure flavor and heat of the specific chili used.

Chili Powder (Spice Blend):

This is a blend of ground chiles and other spices.1
Common additions include cumin, oregano, garlic powder, and sometimes other spices.2
This is the typical "chili powder" found in most grocery stores.
It offers a more complex flavor profile than just ground chiles.3

Therefore:
No, chili powder (the spice blend) is not the exact same thing as ground dried chiles.4
Ground dried chiles are a component of chili powder blends.5
In essence, if you grind dried chiles on their own, you have ground chiles. If you add other spices, you have a chili powder blend.