Why UnrealBuildTool tries to recompile the engine on building a Game Module?

Debian 10

I have pulled a source code,
$ ./Setup.sh,
$ ./GenerateProjectFiles.sh
$ make

It generated a lot of binaries, and I can run UE4Editor, which is cool

next I tried to create a C++ Project, and after it tried to start it, said i need to recompile game module… Cool… and it failed said I need to do it via ide… cool…

One more attempt to run project via editor from terminal:

###$ …/UnrealEngine/Engine/Binaries/Linux/UE4Editor /home/uname/Projects/ue4/SampleProject/SampleProject.uproject

and it failed with same reason, and I noticed the command to build which is seems legit for me

< mono init here >
/home/uname/UnrealEngine/Engine/Binaries/DotNET/UnrealBuildTool.exe Development Linux -Project="...path .uproject" -TargetType=Editor -Progress -NoEngineChanges -NoHotReloadFromIDE

-NoEngineChanges seems legit as well

but what happens next is it said
Building would modify the following engine files:
and next is a few pages of engine binaries and libraries…

I can try to run build without -NoEngineChanges and probably it would run. but i wondering why it is happens??

Also I have noticed there is some weird directory inside Intermediate

./UnrealEngine/Engine/Intermediate/Build/Linux/B4D820EA/

which by itself took 32Gb

$ du -h --max-depth=1 ./
32G	./B4D820EA
2.0M	./UE4Game
8.0K	./UnrealInsights
8.0K	./UnrealLightmass
8.0K	./UnrealFrontend
160K	./UnrealHeaderTool
284K	./CrashReportClientEditor
276K	./CrashReportClient
8.0K	./UE4Editor
8.0K	./ShaderCompileWorker
32G	./

and inside it looks like

$ ls
BenchmarkTool          CrashReportClient        DatasmithMax2016       HeadlessChaos        TestPAL    UnrealCEFSubProcess  UnrealInsights         UnrealRecoverySvc
BlankProgram           CrashReportClientEditor  DatasmithRevit2018     LiveCodingConsole    UE4        UnrealFileServer     UnrealLightmass        UnrealVersionSelector
BootstrapPackagedGame  DatasmithCADWorker       DatasmithSDK           ShaderCompileWorker  UE4Editor  UnrealFrontend       UnrealMultiUserServer
BuildPatchTool         DatasmithFacadeCSharp    DatasmithSketchUp2017  SlateViewer          UE4Game    UnrealHeaderTool     UnrealPak

One more small detail, initial build was done inside debian:10 container in docker.