yeah that's right. some belgian brewers use something called open fermentation to brew. it lets in wild yeasts that add a character to the beer that is world renowned. open fermentation is not for the inexperienced though. there's a lot of debate on open vs closed fermentation and some debate about what exactly distinguishes open from closed fermentation. you're exactly right. beer has been around for literally millenia longer than anyone has had any concept of bacteria or infection.
anyway with regard to your question about the airlock. after you pitch your yeast and put the lid on, the four days following that will see the most active respiration and fermentation of the yeast. within 8-12 hours after yeast pitching, you'll start seeing the airlock pop bubbles every few seconds. what's happening is that the yeast is working through stage 1 of the yeast cycle - respiration, where the yeast cells build up energy in prep for fermentation and develop new cells throughout the beer. respiration is fast, measured in hours and usually less than a day. the 2nd yeast cycle stage is fermentation, where the action is. this is where the yeast begins rapidly feasting on the sugars in the wort (now beer technically) and converting them to CO2 and, oh yes my friend, alcohol.
what i suspect you are seeing with the water piling up on the side of the airlock is the beginning of fermentation. co2 is starting to build up in the primary fermenter. soon you'll start seeing that airlock bubble every few seconds. this is the co2 being released through fermentation. by tomorrow i expect you'll be seeing these bubbles.
expect those bubbles for about 4 days. after that it will stop. at that point, just leave the fermenter alone for 10 days, then bottle.