Yes I know Bitcoin and bitcoin difference but it does not matter unless you like to really specify the right use of grammar. Here in our place where English is not our primary language, most or all people I know here does not matter when it comes to using the right word. Bitcoin is a noun and that itself could be use to name the system.while.bitcoin is a system unit wherein the smallest unit is satoshi.
I just do not pay attention between the difference of the two in writing. It depends on the usage of bitcoin, as a currency or blockchain. What matter is how to work on it to gain and earn it, then use it on the market or any transactions.