Earlier quoted context omitted.
Since the whole idea of ‘opt in’ is choosing to do something, the only reasonable interpretation of ‘opt in by default’ is that the default state requires you to make the choice yourself. However I try to bend my brain, sing the term ‘opt in’ for the exact opposite makes no sense whatsoever. Note that I’m not using English grammar as my argument; human language (and English especially) has plenty of exceptions and ex…
I read it as though he was trying to say '[you are] opt[ed] in by default'. Now granted, he did not say that, and I only reached that conclusion by the rest of this conversation, but I think to have meant that and said '... was now also opt-in by default...' isn't unreasonable. Just sharing since you mentioned you couldn't see how using that term for the opposite would make sense.
"Opting someone else in" is essentially the same category of error as "consenting for someone else". People can only consent for others in specific circumstances and even then only for specific people (e.g. legal guardians), trying to argue "but I consented for them!" in front of a judge usually ain't gonna work.