Cannot 'implement' Person from class

When I try to implement 'Person' on a class like:

```JS
import { Person as PersonSchema } from 'schema-dts';
export class Person implements PersonSchema { ... }
```

TS errors with
```
A class can only implement an object type or intersection of object types with statically known members.
```

Which can be solved by editing this snippet:
```JS
export declare type Person = ({
"@type": "Person";
} & PersonBase) | Patient;
```
to
```JS
export declare type Person = ({
"@type": "Person";
} & PersonBase);
```

Obviously, this case is true for any type declaration in the pattern `(...) | [TYPE]`. The same applies to extending interfaces.
What is the reason for this pattern? Is it intended?