Help understanding routing with a custom `_routes.json`

Hey I'm debugging an user bug report for Astro.
The user has the following

_routes.json

_routes.json

_routes.json

_routes.json

{
  "version": 1,
  "include": [
    "/404",
    "/_image"
  ],
  "exclude": []
}

{
  "version": 1,
  "include": [
    "/404",
    "/_image"
  ],
  "exclude": []
}

{
  "version": 1,
  "include": [
    "/404",
    "/_image"
  ],
  "exclude": []
}

{
  "version": 1,
  "include": [
    "/404",
    "/_image"
  ],
  "exclude": []
}

And the following file-tree:

dist
├── _redirects
├── _routes.json
├── _worker.js
├── favicon.svg
└── index.html

dist
├── _redirects
├── _routes.json
├── _worker.js
├── favicon.svg
└── index.html

dist
├── _redirects
├── _routes.json
├── _worker.js
├── favicon.svg
└── index.html

dist
├── _redirects
├── _routes.json
├── _worker.js
├── favicon.svg
└── index.html

If he now tries to access his webpage using the following url:

https://example.com/unknown

https://example.com/unknown

https://example.com/unknown

https://example.com/unknown, the

index.html

index.html

index.html

index.html is returned.

Would like to understand the why, so we can offer a fix in Astro?