First, let's take the old terms. App Store guidlines point 3.1.3 from 2020-11-28: [1]
Apps in this section cannot, either within the app or through communications sent to points of contact obtained from account registration within the app (like email or text), encourage users to use a purchasing method other than in-app purchase.
The old rules seem pretty straightforward. You're not allowed to contact users about other payment options if you acquired the contact info through the app.
Now, the press release from 2021-08-26 says: [2]
Apple is also clarifying that developers can use communications, such as email, to share information about payment methods outside of their iOS app. [..] Users must consent to the communication and have the right to opt out.
This seems like it's purposely vague. The press release doesn't talk about the source of the contact information at all.
So let's take a look at the updated terms. App Store guidelines point 3.1.3 from 2021-08-25: [3]
Apps in this section cannot, within the app, encourage users to use a purchasing method other than in-app purchase. Developers cannot use information obtained within the app to target individual users outside of the app to use purchasing methods other than in-app purchase (such as sending an individual user an email about other purchasing methods after that individual signs up for an account within the app). Developers can send communications outside of the app to their user base about purchasing methods other than in-app purchase.
What a bizarre paragraph. First it explicitly makes it clear that it's forbidden to send the payment information using contact information obtained via the app. However the last sentence is a generic statement that seems to contradict that. Does Apple mean that you can only use contact information obtained elsewhere? That would then match the previous terms. So it's probably that. However it is worded in such a horrible way that I can't be sure.
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After looking more into it, I think some actual changes might still be coming. Here's the key paragraph from the actual court document: [4]
Apple has agreed to revise its App Store Guidelines to permit developers of all app categories to communicate with consenting customers outside their app, including via email and other communication services, about purchasing methods other than in-app purchase. See Berman Decl., Ex. A at § 5.1.3. Under the App’s Store existing Guidelines, developers may not use contact information (emails, phone numbers, etc.) obtained within an app to contact their user base outside the app. As a practical matter, this prevents developers from alerting their customers to alternative payment options. The proposed Settlement lifts this restriction, and it does so for all app categories.
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[1] https://web.archive.org/web/20201128030647/https://developer...
[2] https://www.apple.com/newsroom/2021/08/apple-us-developers-a...
[3] https://web.archive.org/web/20210825162013/https://developer...
[4] https://s3.documentcloud.org/documents/21049923/apple_propos...