Speaking as a boring cishet guy, I know it would have taken some major, science fiction-level brainwashing to get me to stop liking the girls I went to high school with, and/or start being interested in the boys. “Societal pressure” would not have been nearly enough.
It’s much more humane, and kind, to simply accept and support people.
I use to think I was cis and het too. Up until my late 20's. Turns out I was wrong on both. Still don't think we should start assuming people who say they are cishet are just delusional though.
I didn't figure out I was nonbinary and asexual until my mid twenties. I had an entire gender crisis in high school too. But at the time I didn't know either were things you could be so I'd just concluded that I was cis, but that I was deeply uncomfortable with the expectations society puts on boys/men.
When I was in high school, I was confused how other autistic people could be trans because I couldn't understand how they'd have a gender without buying into the socially constructed bit. So me considering myself technically cis-by-default was primarily because of not knowing agender was an option.
In terms of sexuality, I preferred that some people thought I was gay and I had even considered I might be some sort of ace-spec, but didn't realize horny ace was an option and probably mistook some envy and non-sexual attraction as sexual attraction.