Game on disc, why installing from internet

Hey there.

I’ve bought an Xbox One today, Elite version with 1 TB hard drive and of course with Halo 5.
I live in Europe and I have region set to United Kingdom, but I doubt that has anything to do with my problem.

The problem is, that when I updated console, logged in and all that stuff, I insterted Halo 5 into console and started installing it.
Everything should be fine right? Well not exactly…
The game installation were really slow, so I checked internet what can be the problem.
Ok, I saw that I have to download 9 GB patch, sure not a problem. I left console for an our or two.
When I came back I saw that I game is still installing and I have downloaded like 24GB, just wow…
It was like on 35% progress on installing.
I’m assuming that the whole game was downloading from the store, but the question is…why?!

I read that best option is to turn console offline and than install the game and after that install patch.
I’m doing this right now, but I wasted so many time and bandwitch for this that I’m furious right now…

Why game wasn’t installing straight from the BD disc and instead it was downloading from the internet?
I would like to avoid something like that in the future, so maybe somebody had the same problem?

you must disconnect from the internet before installing it then reconnect once its started

So the games will always be downloading first instead of installing from the disc if I’m online?
That’s kinda ridicoulous, don’t You think?