I had a similar experience as well. I saw people argue that the change from -sexual to -gender was because "sexual" was an ambiguous term that could either refer to sex (the activity) or sex as in gender. So to avoid confusion and especially to stop trans people (trans women in particular) from being associated with shemale porn (which back then was arguably the type of media where trans people were the most visible and which painted trans-women as hypersexual beings - ironically true in hindsight) people wanted to switch to trans-gender. The entire gender=culture idea really only came afterwards, and at that point people suddenly pretended like that was the reason for the change in terminology. Another case of the trans community engaging in revisionist history.