Wikipedia is only a source of concern if the primary sources it cites are unreliable, in the linked article they refer to ABS data which is the most accurate population data for that country. No LGBT question was asked in the more recent Australian census. The ~4% of population being homosexual was a talking point during our same sex marriage plebiscite, hence why I use it.

However, in recent US census data 3.3% of the population respond as being Lesbian or Gay, with 4.4% bisexual https://www.census.gov/library/stories/2021/11/census-bureau-survey-explores-sexual-orientation-and-gender-identity.html. It'd be interesting to see how that percentage progresses as majority of positive respondents were in younger generations, while I doubt any will go from identifying as gay to then straight, we may see a decline in those who identify as bisexual as they age...but who knows.

Regardless, returning to the OC, the figures for trans were all around the 0.6 mark in most sources I saw, so the 2/400 in the OC is accurate.