Pequin are about that size but I never saw them grow in clusters. I have heard of African Bird Peppers growing in clusters. There are Thai peppers that grow in clusters but the pepper is larger. It could be a hybrid of an Etna pepper as they grow in clusters. Where did the plants come from? A local nursery?
Piri Piri is a type of African Bird Pepper but they can grow to two inches in length. There are numerous type of peppers called Bird peppers. They are called that because birds eat them and scatter the seeds. I have never grown then but to me the pepper looks to be an African Bird pepper.