He said 8GB was decided "early on in the process", not "At the beginning". When I started working on the project, and for months afterwards, there was less RAM. Some of my coworkers had been working on it for months before I got pulled in. Now this is still about 2 years before launch, so it can easily be classed as an "early" decision. But when I started, everything else, including ESRAM, HDMI in, and, at first, no optical drive, was already in the design.
The ESRAM is a logical evolution from the 360 design, why would anyone think it had been forced on the designers due to some other influence, like the amount of RAM?
I'm pretty sure my recollections in this case are correct, because I asked questions about it at the meeting where we announced the project to a larger group of employees, in January 2012. I asked three questions, one about the amount of RAM and reservation, one about how they were approaching the (then) rumors that pointed at the PS4 being significantly more powerful, and one about how they were going to pitch an online only console with sales targets in the hundreds of millions, to the majority of consumers that had capped internet.