Jack didn't actually remember Lucas mentioning the part about not entering Layla vaginally, but was glad it had been stated again. He'd probably been too busy being stunned at being asked in the first place to remember the details.
As for the slave part...
"Not a concern, Layla. I've been Dom, Sub and no games at all. I don't mean to be difficult when I say that I really don't mind what you'd like to do. I can't imagine you have something in mind that I would disagree to."