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I can’t answer the detailed “how”, but it is shorthand for handling resource outputs which need to be resolved before use.
See <https://www.pulumi.com/docs/intro/concepts/inputs-outputs/>
The specific doc page for interpolate: <https://www.pulumi.com/docs/intro/concepts/inputs-outputs/#outputs-and-strings>

Yes. That’s where I came across this functionality.

If you're asking about the js syntax, it's called a <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals|tagged template literal string>
&gt; _Tagged_ template literals call a function (the _tag function_) with an array of any text segments from the literal followed by arguments with the values of any substitutions, which is useful for <https://en.wikipedia.org/wiki/Domain-specific_language|DSLs>