The answer to 'how did mosquito get in my house' is that mosquitoes can easily find their way inside through small openings and cracks in windows, doors, and screens. Mosquitoes are attracted to the warmth and carbon dioxide exhaled by people, as well as standing water where they breed.
To prevent mosquitoes from entering your home, make sure all windows and doors have tight-fitting screens without any holes or tears. Seal any cracks and openings around utility pipes, vents, and other entry points. Eliminate standing water sources like clogged gutters, birdbaths, and pet bowls. If you still have a mosquito problem, you may need to call a professional pest control technician to identify and treat the source.