It's only 30% if you are around people who are from Gen Z exclusively. The overall percentage is lower.

“In its most recent poll, released in February of last year, Gallup found 7.2% of adults in the U.S. identify as LGBTQ, including nearly 20% of those in Gen Z, which that survey defined as those ages 19 to 26.”

The point is to show that newer generations, especially Gen Z, are identifying as LGBTQ+ at a higher rate than previous generations. That being said, it wouldn't surprise me if the numbers are lower for past generations because there are more dead and closeted LGBTQ+ people in those generations.