The answer to 'how did silverfish get in my house' is that silverfish are common household pests that can enter your home through small cracks and crevices. They are attracted to damp, humid environments and feed on things like paper, glue, and starch-based foods. Silverfish can also come in through doors, windows, and other openings, especially if your home has poor sealing or insulation.
Silverfish are nocturnal and prefer to hide in dark, undisturbed areas like bathrooms, basements, and attics. They reproduce quickly and can be difficult to get rid of once established in your home. Signs of a silverfish infestation include seeing the insects themselves, as well as small holes or damage to paper products, fabrics, and other household items.