Not quite. The LGBT initialism only includes lesbians, gay people, bisexuals, and trans people. It doesn’t include asexuals, pansexuals, or intersex people, just off the top of my head. I don’t imagine many people will correct you for just using LGBT, but it can be more inclusive.

This actually makes a lot of sense. A lot of people are using Lemmy either because they prefer federated web platforms to centralized, which makes it antithetical to corporate interests, or because they’re opposed to Reddit’s API policy, which was a blatant move to squeeze more money out of their users. Either way, Lemmy’s appeal is very anti-capitalist, and since opposition to capitalism is a generally left-wing philosophy, I can totally see why most Lemmy users would be left-wing.