The article says they spend around $150k/year on infra. Given they have 8 DevOps engineers I assume a team of 50+ engineers. Assuming $100k/engineer that's $5 million/year in salary. That's all low end estimates.
They saved $100k in the move or 2% of their engineering costs. And they're still very much on the cloud.
If you tell most organizations that they need to change everything to save 2% they'll tell you to go away. This place benefited because their previous system was badly designed and not because it's cloud.
I'm not making an argument against the cloud here. Not saying you should move out. The reason why I call out cloud infrastructure specifically is because of how easy it is to let the costs get away from you in the cloud. This is a common thread in every company that uses the cloud. There is a huge amount of waste. And this company's story isn't different.
By the way, 8 DevOps engineers with $150k/year cloud bill deserves to be highlighted here. This is a very high amount of staff dedicated to a relatively small infrastructure setup in an industry that keeps saying "cloud will manage that for you."