It must have been a hybrid chili. When they self pollinate the genes re-assort to show different characteristics. The chilis shown may be unique to your garden.

The photo looks like birds eye chillies. But welcome to the world of nature. The problem with just about all seeds taken from a plant is that they will differ from the mother plant. Unlike a cutting that will contain the same DNA and be an exact copy of the donor plant, seeds will produce different attributes. In the case of hybrids, some will revert back to the original plant before it was hybridized or crossed with another plant and some will sort of mutate and create a different type.

The best way to explain it is that growing plants from seed is similar in human terms when a baby is born. It would most likely have brown eyes if both parents have brown eyes but could also be born with blue eyes. Likewise, it could go into adulthood to be tall, short, blonde, etc.

So the bottom line is, don't be dismayed at what you have grown from your seeds. it's part of the fun and excitement of seeing what you eventually end up with. You never know, you could even end up with a new type of chilli. A long time ago someone just planted an apple pip for fun. This developed into a new species of apple and the Granny Smith was born.