The description of the second last one gives a quite good explanation. That, combined with a huge amount of patience and craftmanship I assume.

I may deal with the playing cards but I am still curious how to put the wood board into the bottle. :-O

There is a trick where you can wet wood for a very long time and it becomes more malleable. This lets you do things like, place a solid metal beating within a single hunk of wood.

https://www.youtube.com/watch?v=qO7aFRO5WMw

Probably not how it was done, but is it possible to craft a bottle in such a way that the refraction index makes the content appear larger than it actually is?

This guy seems to have a pretty good idea: https://news.ycombinator.com/item?id=7862320

Very carefully...

More seriously, note that he only claims the bottle hasn't been cut/modified, nothing about the objects within. To me, it's rather obvious that they're disassembled into pieces small enough to go in, then reassembled inside. Reassembly is the tricky part but it's not hard to see how things could be manipulated into position with string (or dental floss as he mentions), tweezers, sticks, and other tools.

There are some good videos of doing it on YouTube too.

(Also I observe that the "proprietary trade secrets" in this "industry" happen to be the complete opposite culture of the open-source/open culture/information sharing movement...)