I think they mean what in lodash was _() and .values(): You could not execute map or filter on an array. Instead you needed to wrap it in a lodash object using _(arr), that you can call .filter() on. To get the filterd values out, you call .values() on its result. You could also do _.filter(arr, …). To me it became confusing when I needed to use .values, and when nesting it got worse.

LINQ has instead methods on its types that partially returns builders. I find that easier to use, and using C# type system it calculates the result types for me.