It's hard to overstate how absurd this is as you work through the implications: it means this business model is in conflict with the obvious goal of growing the ecosystem of verified creators as quickly as possible, and assumes incredible ignorance from the Brave team about likely revenue from users unwittingly donating to unverified creators.
The reality is without creators actively pushing their supporters to donate to them via Brave's rewards system the funding flow would largely be Brave 'promoters' pushing creators to use that funding channel.
Instead of this nonsensical explanation it's easy to understand the simple and correct one: Brave had an aggressive growth marketing strategy where they imagined being able to email unverified creators with emails about how much $$$ they could collect from users who had started donating to them, and in doing so accelerate verification of creators.
The stupidity here is that they didn't properly consider that some creators would rightly object to an implication Brave Rewards was an approved donation channel for that creator, which could theoretically risk cannibalising donations that would otherwise go through other channels (that it would likely be a negligible amount doesn't make it any less unethical). Brave did the right thing in fixing it in an early public beta, which is the point of public betas.
Your second criticism about user agent spoofing depends on a fundamental lack of awareness about the whole history of user agent strings, which is basically a story of challenger browsers spoofing the user agent string of the dominant browser within an ecosystem for compatibility reasons [0].
That you attempt to assert that UA spoofing is a nefarious practice (but presumably only for Brave, not for every other browser that does this, such as Chrome for Android which presents as Safari[1]) is yet more evidence of the low credibility of these criticisms.
[0] https://en.wikipedia.org/wiki/User_agent#User_agent_spoofing