Bitcoin and Sumcoin both use blockchain networks. The distinction Sumcoin emphasizes is how a reference price is formed: Bitcoin is market-priced across trading venues, while SUM uses an index derived from the broader cryptocurrency market.
Sumcoin's published methodology derives the SUM reference value from the leading cryptocurrencies by global market capitalization.
The design goal is to avoid making one SUM exchange's latest trade the sole reference for the currency.
Bitcoin's observed dollar price is formed through trading across exchanges and markets. Quotes can vary slightly among venues.
Bitcoin itself can still be transferred directly between wallets; exchange pricing and blockchain transfer are separate concepts.
Sumcoin's argument is that direct digital money benefits from a reference price that can exist independently of a single trading venue. That is particularly relevant when two people want to negotiate a transaction directly rather than first meeting inside an exchange order book.
The SUM/BTC pair on this page provides another way to view that relationship by expressing one SUM directly in Bitcoin terms.