Diego had made a promise to Annie to not hurt The Deep. He fully intended to keep that promise. However nothing was said about not watching while other people hurt The Deep. It was a loophole, and he knew it, but one he fully intended to take advantage of.
She probably shouldn't have told him that the asshole got transferred to Sandusky today.
He hadn't fully explained to Steve why he had brought Five along to their little adventure, but he figured the situation would explain itself soon enough.
"Okay, so, I figure we pretend Five is a fan," Diego said as the elevator dinged to let them off on the upper floors. "And we're just his exasperated guardians letting him meet his hero."
He said 'guardians' like he didn't know he would yet again be mistaken for Five's father. At least Steve also now had to deal with being one of Five's dads this time.
[For a few!]