The relation of it will depend on how much he has bought that bitcoin on his account. If it's during the high and he's got stuck there with 1 bitcoin, it matters a lot to that gambler. He can withdraw it and still get 1 bitcoin but the current price of it matters because it's no longer the same as high as it was during his purchase. That's the actual matter of it but if a gambler uses most of the time altcoins, then there's also the same relation on it but there is the feeling on how easier it is to gamble with those.
Maybe those who gambled using Bitcoin he bought it at the high Bitcoin price at that time, and maybe he did it because he saw the Bitcoin price was going down.
And in my opinion there is no need to gamble and bet using your Bitcoin, it is very ineffective to do, it is better if you want to gamble bet with the dollars you have or with other altcoins even though now the market is down as well as the price of the altcoins, this is not too hard to do when compared to risking Bitcoin, don't just because the price of Bitcoin is decreasing don't let you be fooled by this.