After the resonance, everything from his physique to his senses to his energy reserves had skyrocketed. And so because of this, Gideon sensed something, he sensed that they were being watched.
However, he didn't address this issue immediately as he simply dealt with the remaining ships that survived the onslaught.
After that, he used Lisk gravity to essential bind the space and prevent any more ships from coming through. It was only after he had done all of this that he turned to look in a certain direction.