If it weren't for the fact that everything about Lust was oozing from the pores of her skin, he probably wouldn't have recognised her. That about described the relationship between the two most arguably distant Sins. He hardly knew anything about her, she probably didn't know anything about him - sometimes they didn't recognise each other's appearances and had to rely on familiarities which, to everyone else, made no sense whatsoever.
Something about her had changed - he wasn't quite sure what it was, but she simply felt different. She was not the Lust he was used to having around, and yet he could not quite put his finger on a reason why. It could have been any number of things - perhaps childbirth did strange things to women, or her trip down to hell altered her in some way. Maybe her not immediately trying to work her ways on him or making some snide comment about him or something inappropriate about Envy and himself was throwing him off.
For some reason, he felt like she was afraid of him. And while Lust was always wary of Pride, she was never afraid of him.
The fact that he thought any other Sin standing here in his position would pick it up straightaway did nothing to alleviate the... strangeness of the situation.
"You look well," he said when he was standing before her, his voice sans emotion, his face sans expression.