From the article:
The user is given the option to enable or not enable Siri, Apple's virtual assistant. But enabling only refers to whether you use Siri's voice control. Siri collects data in the background from other apps you use, regardless of your choice, unless you understand how to go into the settings and specifically change that,’ says Lindqvist.
You're right, I somehow missed that paragraph — I swear I read the article before commenting.
Not condoning or anything, but perhaps the thinking is that, if the user can re-enabling siri at a later date, they don't want siri to start with no memory?
If/when a user actively consents to "learn from app", it's no different than setting up a new device, e.g. mail downloaded from IMAP server, data transferred from old device, or from cloud services.
Now imagining a EULA for Helpful Pre-Stalking..
Why would you think that?
If I enable some personal assistant at some point in time, I absolutely do expect it to start with no memory.