Unfortunately, this is true, and a lot of people struggle to manage their diabetes after switching to the Walmart brand. The stories I have heard generally occur to young adults who have to transition out of their parents' insurance plans.
This article is from 2019 and is out of date. It's saying that Walmart only sells human insulin which isn't true any more. ReliOn NovoLog is a modern, analog insulin and is exactly the same as "regular" NovoLog:
https://www.walmart.com/cp/relion-diabetic-care/3769564