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.