Part of this question basically seems to be asking if the answers to the other question are actually right. For that part, don't worry — they are. (And no information is lost in this way — the leader of your course is wrong. *)

The other parts of the question basically ask if (and why) this information is stored at all, if it doesn't affect the raw data.

The answer is: like many camera settings other than the fundamental exposure factors (shutter speed, aperture, and sensor gain/iso), the color space selected is stored as advisory information, so that you can make choices in-camera and have them reflected as defaults in RAW processing software. This might not make a lot of sense with color space, but consider tone curves (or even black and white mode), white balance, and even crop. None of this is baked into or affects the basic RAW data itself, but all can be useful to have later.

Keep in mind that Adobe RGB is not strictly better than sRGB — that's a common myth. This is especially true in 8-bit images, like JPEGs. See What's the difference between Adobe RGB and sRGB and which should I set in my camera? for more — but, again, don't worry about it when using RAW. A greater concern is that your camera's rear LCD (or EVF, in mirrorless) is likely to be calibrated to show sRGB correctly, and using Adobe RBG may actually result in less correspondence between what you see there and what you're actually capturing.

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* except possibly with the very minor theoretical effect you might see from possible biased metering, as explained in my answer to that other question.