As cryptomania ramped up last year, we saw a lot of hype around bitcoin - the currency.
Note the use of the lowercase "b". The second usage "Bitcoin" is a reference to the ecosystem and is more focused on the Bitcoin protocol as opposed to the currency.
I might say, "I paid 0.2 bitcoin for xyz" if I wanted to specify the exchange of bitcoin tokens.
The distinction is small, but important. There's no certainty bitcoin will remain the defacto cryptocurrency of the future. However, it's undeniable that Bitcoin paved the way for new ways of thinking, as well as, stronger and more adaptable tech.
bitcoin = the tokens that you can exchange and live on the blockchain
Bitcoin = the tech ecosystem (protocol and payment network) that supports bitcoin