Why the RedisVectorStore adds a prefix

import redis

from llama_index import (
    StorageContext,
    DocumentSummaryIndex,
    load_index_from_storage,
    ServiceContext,
)

from llama_index.storage.docstore import RedisDocumentStore
from llama_index.storage.index_store import RedisIndexStore
from llama_index.vector_stores import RedisVectorStore
from llama_index.embeddings import HuggingFaceEmbedding
from llama_index.schema import Document


REDIS_DB_HOST = "localhost"
REDIS_DB_PASSWORD = ""
REDIS_DB_PORT = 6380

redis_client = redis.Redis(
    host=REDIS_DB_HOST, password=REDIS_DB_PASSWORD, port=REDIS_DB_PORT, db=0
)


docstore = RedisDocumentStore.from_redis_client(
    redis_client=redis_client,
    namespace="Fail_doc_store",
)
index_store = RedisIndexStore.from_redis_client(
    redis_client=redis_client,
    namespace="Fail_index_store",
)
vector_store = RedisVectorStore(
    redis_url=f"redis://:{REDIS_DB_PASSWORD}@{REDIS_DB_HOST}:{REDIS_DB_PORT}/0",
    index_name="Fail_vector_store",
    index_prefix="llama",
    overwrite=True,
)
storage_context = StorageContext.from_defaults(
    docstore=docstore, index_store=index_store, vector_store=vector_store
)

service_context = ServiceContext.from_defaults(
    llm=<SOME_LLM_MODEL>,
    embed_model=HuggingFaceEmbedding(
        model_name="intfloat/multilingual-e5-large",
    ),
)

document = Document(text="This is a test document", id="test_id")
index = DocumentSummaryIndex.from_documents(
    documents=[document],
    storage_context=storage_context,
    service_context=service_context,
)
index_id = index.index_id
index2 = load_index_from_storage(
    index_id=index_id, storage_context=storage_context, service_context=service_context
)
query_engine = index2.as_query_engine().query("This is a test query")

Traceback (most recent call last):
  File "/Users/HASHKELL/SHERPAS/Funds/fundssociety-rag/recreable_fail.py", line 56, in <module>
    query_engine = index2.as_query_engine().query("This is a test query")
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/HASHKELL/Library/Caches/pypoetry/virtualenvs/rag-IF6y9IJD-py3.11/lib/python3.11/site-packages/llama_index/core/base_query_engine.py", line 40, in query
    return self._query(str_or_query_bundle)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/HASHKELL/Library/Caches/pypoetry/virtualenvs/rag-IF6y9IJD-py3.11/lib/python3.11/site-packages/llama_index/query_engine/retriever_query_engine.py", line 171, in _query
    nodes = self.retrieve(query_bundle)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/HASHKELL/Library/Caches/pypoetry/virtualenvs/rag-IF6y9IJD-py3.11/lib/python3.11/site-packages/llama_index/query_engine/retriever_query_engine.py", line 127, in retrieve
    nodes = self._retriever.retrieve(query_bundle)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/HASHKELL/Library/Caches/pypoetry/virtualenvs/rag-IF6y9IJD-py3.11/lib/python3.11/site-packages/llama_index/core/base_retriever.py", line 224, in retrieve
    nodes = self._retrieve(query_bundle)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/HASHKELL/Library/Caches/pypoetry/virtualenvs/rag-IF6y9IJD-py3.11/lib/python3.11/site-packages/llama_index/indices/document_summary/retrievers.py", line 176, in _retrieve
    node_ids = self._index_struct.summary_id_to_node_ids[summary_id]