Fair enough. It does say "may". :) It's still possible for other data to be "anonymous" if it's stored independently of an IP address, device identifier, etc. since recital 26 allows for data that is "no longer identifiable".
Then again, they had it when you downloaded the update, and when your devices check for auto update, so, you’re not getting away from this data collection with an opt out button.
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A person is identified, if the ID references only one user in the whole dataset[1]. This also makes any information linked to the ID PII.
the ID would be pseudo-anonymous if one would need some extra data, to which they don't have access to, for linking the ID to one specific user in the whole dataset[2].
So to answer your question, RTB ID is not pseudo-anonymous as it only references a single user out of all of them.
[1] It's also important to understand the definition of PII in GDPR context. Which is any data that relates to an identified or identifiable person. Identifiable is the same as distinguishable. Knowing this helps to understand where the line is. https://www.lexico.com/en/definition/identifiable
[2] Definition of pseudonymisation, 5'th bullet-point: https://gdpr-info.eu/art-4-gdpr/ sheds some light on this.