Actually it does. I can enter a raid solo, but I won't be able to do much. I can enter with a small group, and we can clear trash and maybe get epic items.
Why is it I get the feeling you are hoping they change their mind about Adventure zones = Raids? They won't. The fact they aren't in game at launch means nothing, except they need more time to work on them, and they won't be important for leveling and early end game. Its pretty obvious where this is going, don't ya think....
Yes you can go into AZ as a solo player or as a small group, but you won't be able to clear it all. It doesn't scale depending on the group size. So if you go in solo you might only be able to kill like a few mobs here or there, but can't take on groups or bosses. And if you only go in with a normal group (4 people) it might be good enough to take on a few pack of mobs but not bosses.
So in case of the jackashflash its obvious he is coming from WoW. Indeed you can enter blizzards raids in smaller number than intended, but you wouldnt be able to kill any of the bosses and get any loot (no 0.01% drops doesnt qualify). Different concept
In Adventure zones, according to what we have heard from developers, there would be a lot of different content ranging from solo to large groups, means REWARDING encounters for single player, group, multiple groups. Try think of it as large zone with multiple world bosses (speaking in WoW terms in attempt to make it more familiar to you), designed for various amount of players. They wont be exclusive instances either, so there can be multiple teams taking on smaller encounters and perhaps even dynamically join forces to overcome big one. There is no "mob tagging" as you know it either, so joining battles would be easier. That is all we know now and sorry to disappoint, its really not "raid" in blizzard terminology
Please keep in mind developers literally said "adventure zones are still being designed" and "they will not be included at launch", that is the only and most recent info we have