Most type checking happens at runtime (this might not be true for interfaces at some level, but I can’t say for 100% certain - I just know I tend to see interface related errors earlier during code execution…). It’s perfectly valid syntax to declare a private method as returning an integer and then for the body of the method to return a string (explicitly cast as a string even). As long as you never call that method at runtime, no exceptions will be thrown.

With a half decent IDE or LSP, these sorts of runtime exceptions can be easily avoided but technically they still exist and if you don’t know about that, it can be argued to be confusing. PHP has made a lot of trade-offs to largely maintain backwards compatibility and many of them live in decisions that happen at runtime.

Modern PHP tooling can provide type safety in a very similar way to Typescript if you’re willing to put in the effort while also still technically offering you an escape hatch to do whatever the heck you want and duck type to your hearts content.