The blog has a typo. The first line needs to have the text in uppercase:

> query WHERE name = ‘ABC’

> create an indexed UPPER(name) column

The point is that the index itself is already on the data with the function applied. So it's not a full scan, the way the original query was.

Of course, in this particular example you just want to use a case-insensitive collation to begin with. But the general concept is valid.