Perhaps this file is just the installer and the actual system files are much larger? Or maybe your 400MB figure comes from a bloated install? Just speculating here.
A compressed download is my guess. The easiest way to predict if an app is using Electron is to see if the download is around 90 to 130 MB. Especially if that size feels unreasonable for the functionality that it offers.
The Electron Framework.framework it contains is 400+ MB alone. I don't understand where you come up with your 90 MB figure?