If you peruse the folder where it's installed and compared to any UE4 or UE5 game, you'll notice all the other similarities in .dll files, folders and whatnot. Even the CrashReporter.exe is the same you see in unreal games. Or you can check the config files at Epic Games\Launcher\Engine\Config which has stuff like BaseEngine.ini which, among other networking configurations, also has this:

[/Script/Engine.Engine]
ConsoleClassName=/Script/Engine.Console
GameViewportClientClassName=/Script/Engine.GameViewportClient
LocalPlayerClassName=/Script/Engine.LocalPlayer
WorldSettingsClassName=/Script/Engine.WorldSettings
NavigationSystemClassName=/Script/NavigationSystem.NavigationSystemV1
NavigationSystemConfigClassName=/Script/NavigationSystem.NavigationSystemModuleConfig
AvoidanceManagerClassName=/Script/Engine.AvoidanceManager
PhysicsCollisionHandlerClassName=/Script/Engine.PhysicsCollisionHandler

Meanwhile, in Epic Games\Launcher\Portal\Config, the "game" part of the launcher, you have DefaultGame.ini and DefaultEngine.ini, the latter's first 2 lines pointing back to the Engine folder: [Configuration] BasedOn=..\Engine\Config\BaseEngine.ini

So, yeah, it's the actual engine. I was going to complain about disk bloat, but my Steam install is currently sitting at 1.3GB and I'm not entirely sure how much of that is from cached stuff. GOG Galaxy is taking ~980MB, but roughly 650MB are from redist installers (MSVC2005, 2007, dotnet, etc), so a "clean" install would be way lighter than Steam or EGS, the latter at 1.1GB on a clean install.

That is ridiculous. Even Electron would have been better...