I think the truly gay portion of the population is much lower than we see today for a variety of reasons.
Probably higher because there is a significant stigma attached to being gay in the aggregate both in this country and across the globe.
I know many gay people, including family, and I can tell you that zero have benefited from a social or professional standpoint by being gay, while 100% of them have experienced at least social trauma and the inability to even communicate who they were to those around them for a significant chunk of their lives due to fear (of many things, rejection, abuse, being cut off, religious persecution, etc).
It's getting better but it's still a problem. When being gay is used as one of the number one insults throughout childhood, and a major part of our population is religiously opposed while nearly half of all citizens are behind legislative and proactive defining away of their right to marry, and across the globe in some of the most populous societies on Earth it is actually a crime, people, understandably, aren't eager to identify as gay when they are not, and gay people stay in the closet and unreported as a result. I don't know one gay person that wasn't closeted at some point. No way are they over-reporting on the balance.