This logic might have held 5 years ago but doesn’t hold now. All the large tech companies are under heavy scrutiny and there are multiple anti-trust cases in play. The US administration appears to be anti-trust friendly, and there are hostile companies deliberately backing as many anti-trust actions as they can against Apple.
It makes no sense to imagine they would play into this for a minor discount on purchasing a trivial app.
It’s just as likely likely that a lawyer and an angry developer think it’s worth seeking a settlement in the current climate.
I agree there are hypotheses by which they could have done this but it’s bullshit to assume they must have done this.