Fix reference to action groups

The original text looks like it was copied from the Action Group extends article.

Author: lfolco

docs/merge_points/extend-data.md

@@ -1,8 +1,8 @@
 # Extend data entities
 
-Extending an action group doesn't affect the existing action group.
+Extending a data entity doesn't affect the existing data entity.
 
-In this example we add a `<click>` command to check the checkbox that our extension added with a new action group for the simple product creation form.
+In this example we update the quantity to 1001 and add a new piece of data relevant to our extension. Unlike merging, this will _not_ affect any other tests that use this data entity.
 
 ## Starting entity
 
@@ -67,4 +67,4 @@ Note that there are now two data entities below.
     <requiredEntity type="custom_attribute_array">CustomAttributeCategoryIds</requiredEntity>
     <data key="myExtensionData">dataHere</data>
 </entity>
-```
+```