It doesn't say that at all - it says that the WH claimed to be "on track" to complete 450 miles of fencing, it says nothing about what was already completed except to mention existing fencing that was replaced.
Here's from a newer article from last month, based on a DHS status report:
"Nearly all 216 miles built since Trump took office replaced outdated or dilapidated fencing. Only about 'three miles of new border wall system [have been] constructed in locations where no barriers previously existed,' according to Homeland Security’s June 19 status report on the wall."
http://www.latimes.com/politics/story/2020-06-23/trump-campaigns-on-border-wall-progress-theres-not-much-of-it |
