In the same way that humans are the only technological civilization on the earth, we're likely the only technological civilization in the universe as well. The time scale of evolution pales versus the time scale of intelligently-directed technology, so as soon as one group develops technology it will near-instantly spread and conquer ever-larger areas of space. In the same way that we've come across other intelligent but non-technological species (primates, whales/dolphins, birds), we'll likely come across other intelligent and non-intelligent species as we conquer the universe in the relatively near future. Maybe even technological civilizations inferior to ours (there's still a small window of opportunity for another civilization to beat us to the punch and take over earth), but we can predict the general shape of those encounters by looking at the history of such encounters on earth (the first being the destruction of neanderthals)
What's funny is this is practically just a restatement of a fermi paradox, except instead of asking "why aren't they here", it takes into account what would likely happen if they were here - we'd be gone