Brew doesn't give you a stable or repeatable install. You can't pin tools to specific versions, they'll get updated whenever you update brew. This is by design and kinda the core ethos of brew. The k8s tooling is generally all meant to have you using the bleeding edge stuff--every tool readme usually says get the latest build from a github release package, brew just effectively does that automatically.

Brew will, by default update everything it manages when you run it.

Depending on your perspective, this is either horrifying and annoying or the best thing since sliced bread.