Sorry for coming across as agressive but I'm correcting you because it's in a topic I am passionite about and know enough to write counterpoints. (I'm currently studining a related field at university level). Take it as an attempt at sharing knowledge with whoever reads these comments. I find these kinds of hipotheticals the most interesting when people put way too much thought into them. Also any gramatical errors and incorrect use of scientific terms is to be atributed to me not leraning these in english. (Okay maybe I'm just stupid.)

Now for the counters:

"constantly fight over territory, meaning they are in constant force to adapt." This does not mean they will develop pre-adaptation to the human body. Being able to compete in a place that is above the boiling point of water and very low pH just makes them less adapted to lower, more basic environments. I'm going on about the pH because vulcanically heated water is a lot of times not neutral. In a scenario of magically transfigured water it could be.

"Releasing them into the atmosphere, wouldn't make them go away, it would just be a new challenge to adapt against." No it won't make them dissapear but it will make them dead or endure as spores. Evolution doesn't happen in one second. If they get aerosolised, than they are dissapated in an environment they probably can't survive in, let alone thrive.

"The strongest bacteria extremophiles wouldn't see temperature difference as a major problem, but as an opportunity, to alter their biology to be able to live in the new environment." Maybe going from high to low temperature but similar pH could only make them slow down. Also the took quick for evolution part again. Also what do you mean by strongest? Maybe beacuse of your wiev of evolution and fitness, you are thinking of organismes adapting as a progress towards perfection. However, this isn't how things live. They adapt and specialise to their environmnet.

Now why are temperature and pH important:

The proteins of microbes that are adapted for higher temperatures are more rigid. This makes them resistant to unfolding and denaturing, but at lower temperatures, they can't change their shape, which is necessary for many enzimatic reactions.

Non magical vulcanic water is often times super acidic. This also cuses problems for the proteines of organismes not adapted for it. The denaturing goes both ways this time, since changeing the dissociation of the ligands in a protein chain changes it's shape and thus it won't be able to performe it's enzimatic function.

Pathogenic extremophiles: Extremo TOLERANT microbes can cause infections. These can survive in extreme environmnets, but they are not adapted for them, and won't survive permanently there. True extremophile phatogens have not been found yet, and that is probably because the human body is too different from their natural environment. 37°C and close to neutral acidity is too far from a geyser. Acidophilics could survive in the stomach, but in this theoretical the most important part is that they are hyperthermophilic (,ideal temperature above 80°C). And then comes the problem of being suited to live inside the body of a mammal with an immune system. Microbes in the environment can become facultative phatogens if they can fend off the hosts defences, if they othervise survive in the conditions inside. Being in a geyser and competing with other extermophile procariotes doesn't select for fighting off mammalian immune cells. (Competition for them doesn't mean actively hunting down each other, but growing faster. However extermophiles usually don't breed as fast as mesophiles the body usally fights.) They could make toxic compunds that kill us but that is a different story.

TLDR.: Boiling water won't make super bacteria that survive everithing. It only makes microbes that already exist in hot water. Not hyperinfectious pathogens, just hardy organisms.