This room was meant to be the location of an E-reader event that was never released. The E-reader was a thing that connected to your Game Boy Advance which would load an event (such as new trainers or new Pokemon. Remember Altering Cave?) onto your cartridge if it scanned the appropriate E-reader card. The E-reader and certain E-reader cards were sold in North America, Japan and Australia and UK (and thus RS/E/FRLG copies from different regions did not have access to E-reader events at all). While the E-reader maintained popularity in Japan throughout the timespan of Generation III, after the English E-reader release for Ruby and Sapphire, popularity dwindled in the aforementioned English-speaking countries. Thus, the E-reader became defunct for English FRLG and Emerald copies.
So, we only ever got a taste of the E-reader in Ruby and Sapphire. However, Ruby and Sapphire has a similar door in Mossdeep City that was able to be accessed in English releases via the E-reader. Upon scanning the appropriate E-reader card, you could enter that door in Mossdeep City and start a three-on-three battle with Pokemon Ranger Clayton. The room in Sootopolis was likely to serve a very similar purpose. Hacking actually allows you to enter the room which is concealing a hiker sprite. If you interact with him, he responds with a load of question marks and then the game crashes (see source for pictures), presumably to instigate a battle that is not coded within the game.
That's the whole purpose of the room. It could actually be many other things but this is most likely the case due to its similarity with the Mossdeep sealed room. But if you want, you could interpret the game crashing as the hiker zombie making you one of his own.
Hope I helped. :)
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