If you go to definition of List<T> you would see the following:
public class List<T> : IList<T>, ICollection<T>, IEnumerable<T>
IList<T> already inherits from both ICollection<T> and IEnumerable<T>.
Wouldn't it have been sufficient if List<T> only implemented IList<T>?
If you looked at the source code:
https://referencesource.microsoft.com/#mscorlib/system/collections/generic/list.cs
You can observe that the signature is:
public class List<T> : IList<T>, System.Collections.IList, IReadOnlyList<T>
This can only mean that the metadata browser de-normalizes the inheritance hierarchy for us.