It took a huge amount of willpower to ask this question to Edward.
Even though Rex seemed to be okay in appearance with meeting him after venting earlier, there was an undeniable other, prominent side of him that felt disgusted to talk or be anywhere near Edward.
His betrayal, siding with the humans knowing what they did still looms in his heart.
But even then, he couldn't let his emotions take control.
Out of the people who were under the Executor's circle, it's an unrefutable fact that Edward is the most accessible. Now that he knew Edward was not fundamentally corrupted, he had to make use of this opportunity to extract information about the Executor.
Regardless of his feelings, he had to do this.
"So you're now another copy of the Executor? Or are you an Ancient Human?" Rex asked.
Edward only replied with a smile, "Enough with this, let's pick up our pace"