From what I understand, patch notes reading is something they always do in Japanese. I think they do this at the same time that they release the patch notes itself (across all supported languages) in text form.

And the venue might be E3 but the 'patch note reading' itself might only be streamed in the Japanese channel (nico nico). The reason is because the developers just happen to be in E3 doing other sorts of presentations (in english), while they release the patch notes. And since they do these stuff anyway, might as well do it in E3 where all their cameras are already set up and stuff.