std.algorithm.canFind behavior difference between arrays and elements

[Arun Chandrasekaran via Digitalmars-d-learn]

I'm trying to find the needle in the hay that's an array of 
strings. So the second assert fails for some reason. Is this 
expected? https://run.dlang.io/is/7OrZTA

```
#!/usr/bin/rdmd
void main()
{
    import std.experimental.all;
    string s1 = "aaa111aaa";
    string s2 = "aaa222aaa";
    string s3 = "aaa333aaa";
    string s4 = "aaa444aaa";
    const hay = [s1, s2, s3, s4];
    assert(canFind(s1, "111"));
    assert(canFind(hay, "111"));
}
```

Why is there a difference in the behavior?