How does bitcoin price fluctuation effects your gambling?
Can this fluctuation be considered as kind of gambling as well?
Yes Bitcoin price fluctuation can influence you betting suppose you had lost 10% of your money and next day price increase by 10% then you are even-steven

Well that rule only applies if and when you decide to sell them, until you don't buy/sell them the bitcoins you have remain of same value, it's only when you exchange them to $ is when you're affected by the price.
For ex. I have 2 bitcoins, I bet and win 2 more, now I have 4 but the price drops to half, did I lose half of my money?? technically yes but only if I decide to sell it then and there, but if I don't I still have 4 bitcoins and there value could go up in future.
But in a way, investing is sort of like gambling in itself therefore it can be said that keeping bitcoins is like a gamble?
Yes right its a gamble itself.