Wow, there is a lot of self righteousness being displayed here. He read back what he heard and ATC failed to pick up the read back, that is on them. Then the next transmission he stated ATC was partially unreadable, indicating possibly weak or unclear transmissions. ATC shares liability in our business and in this case failed to correct the read back. The beginning of the video says it's a combination of frequencies so it's more than likely the aircraft weren't on the same frequency and never heard each others clearances and the controller was on multiple frequencies which probably led to his inattention to the read back. Also, traffic information is often given for opposite direction aircraft that are sometimes up to 20 miles away laterally, so that isn't necessarily an immediate threat. Finally, TCAS is there to fill in these gaps and it only sounded like a TA from one aircraft so they probably weren't as close as it seems.
There was a breakdown in the ATC communication system but it was mitigated by the other systems in place and nothing happened. Bottom line, don't be so quick to judge based on a you tube clip and limited information. It could easily happen to any of you situationally aware airmen.