This was posted by "Working Washington", so it seems reasonable to look at Washington state law: It requires tipped employees to be paid minimum wage. So does the rest of the west coast, including California (where Instacart has it's HQ).

https://www.dol.gov/whd/state/tipped.htm

It is, of course, entirely possible that the worker in question is not on the west coast, but Instacart is still welcome to pay a fair wage even if not required to by law, and Instacart should certainly avoid lying about their business practices either way (from the article: "Even Instacart seems to know how messed up it is to pay workers less when they get tipped more — which is why they’ve denied the practice when speaking to reporters at Business Insider & the Miami Herald.")