I'm going to be honest, at an hour and a half I really don't feel like watching it. Do you know if it generally supports or opposes the article in the OP?
The article takes what he says completely out of context and significantly misrepresents what was discussed. The talk was not a blanket defence of Islamic slavery but largely about how the notion of slavery in general throughout history has been very varied and comparing it with notions of 'freedom' throughout history. For example, while technically a slave, many people have been independently wealthy and politically powerful figures and even slave owners themselves.
Where he said 'it's not immoral for a human to own another' it is in the context of how someone could be technically free, yet oppressed and totally beholden to powerful interests and to all intents and purposes 'owned', whereas a slave could, potentially, be wealthy, powerful and living in luxury due to patronage and unrecognisable from what we associate with slavery.
Historical notions of slavery have been so varied, that the term without further explanation is practically meaningless and talking about the ethics of slavery requires a greater contextualisation because notions of slavery are skewed by how we understand the terms today.
With the 'consent isn't necessary for lawful sex' he was talking about historical fact rather than a personal opinion, which he clearly highlighted. It is in the context of how, traditionally, women had no choice in who they married and comparing this to being, for example, a concubine. In neither situation is the woman rally 'consenting', yet the 2 situations are viewed completely differently. This wasn't to say 'concubinage was great let's reintroduce it', just to compare how people view history from a certain perspective.