I guess what your parent poster is saying is that:

without types, all you have is the variable name to guess what it does.

IDEs help but there's only so much they can do.

Yes that's what I meant. All you have is a variable and IDEs can't figure it all if there's no type on it.

Not just that, let's say even if type is known but some of the methods are generated on runtime than IDE has no idea about it.

That’s not unique to Ruby though, I imagine most dynamic languages fall into this bucket.

Exactly, they do including JavaScript.