He purely disregarded that Reen would not be actually alone during the mission which did not go unnoticed by Reen. Both knew what he really meant but Reen refused to acknowledge his underlying meaning.
Both knew that even if she was with a group of people, these people would have their assigned tasks to do during that mission so they could not really be with her all the time thus his short remark.
He did take into account Wisteria, Hue and Mirly's protectiveness when making this light comment. However, he did deduct that when Reen will be consumed in her own hatred during the mission even if they try to stop her they would have no strength and perseverance in doing so.
In the end as they know the deep hatred she had towards the other party they will eventually not stop her but merely protect which regardless of this could cause her harm in the moment of their hesitation to stop or help her.
But he was different, regardless if she gets mad at him or even points the gun at him at one point of the mission, he will still stop her with his own life regardless. He would not trade the risk in her life as they can still have other chances to extract revenge if worse comes to worst.
With the weird things between them she did not know where he was really in her life so she treated their relationship and his words lightly yet a bit seriously. She also knew the hidden unsaid meanings of his words.
"No worries, I can handle myself. And that theory doesn't apply to everything; I believe it depends on the situation." She said offhandedly
"That's not true; Some things can't be done alone. You should not be afraid to ask for help or to simply start and try new things."
Their conversation seems to be getting out of the main topic but knowing he would not let her off if she ignored it, she thought carefully then answered
"I'm not afraid to ask for help it's just that how can I even have the guts to ask for help if I know I can help myself already? It's something like, how do you expect a person to help someone if they can't even help themselves?"
She briefly paused to recollect her thoughts and stared straight at his eyes as she said,
"Also I'd rather not try some things if it will lead me to nothing and the risk of me to losing everything."
"But how can you say that, you can't have everything or even something unless you start with nothing right?" He challenged
"You can have something but not everything so I can say that something can turn into nothing regardless if it becomes your everything or not. As mentioned, you cannot have everything or even something if there is nothing but if there is already something then that's not actually starting from nothing right?" She challenged back looking highly earnest in her words
They momentarily turned silent as they stared and digested each other's unspoken words.