The difference is that Newcomb’s problem allows you to assume that your (believed) choice of output is guaranteed to be your actual decision.
Post-computation interference only occurs in real-life scenarios (or hypotheticals that assume this realistic constraint), and it is those scenarios where Eliezer_Yudkowsky shows that you should pick a different computation output, given its robustness against interference from your “corrupted hardware”.
The difference is that Newcomb’s problem allows you to assume that your (believed) choice of output is guaranteed to be your actual decision.
Post-computation interference only occurs in real-life scenarios (or hypotheticals that assume this realistic constraint), and it is those scenarios where Eliezer_Yudkowsky shows that you should pick a different computation output, given its robustness against interference from your “corrupted hardware”.