"Substantially assist" means it provides a substantial portion of the code or other assets for the app, saving some time for the app developer(s). As with a human software engineer, initially providing buggy or useless code and then revising it to be correct and usable after some additional prompting, counts as "assisting".

$5,000 total revenue counts, even if it takes many months. Revenue from all revenue sources attributable to the app counts, including in-app advertising.

An app that is merely an interface to a large language model, and is not partially or wholly created by a large language model, does not count.

Question will be resolved by searching on Google and Twitter for evidence of this having occurred, and if no such evidence can be found, posting on Hacker News asking if anyone has done it.