Why didn't Ultra-Edge show 2 spikes? Aakash Chopra on KL Rahul's dismissal

Reacting to wicketkeeper-batter KL Rahul's dismissal in the first Test against Australia, former India opener Aakash Chopra said, "[It was] ridiculous umpiring from the box." "Bat hit the pad for sure…visible confirmation…then why not two spikes on the Ultra-Edge?" Aakash asked. Rahul was given out caught behind by the third umpire after Snicko showed spikes following Australia's review.