You mean, whether they would actually believe you or whether they would use the issue as a pretext for denying a visa irrespective of whether they believe you?

The immigration services (and law enforcement more generally) are widely known (the FBI even issued a report a few years back on the issue on law enforcement generally) to be extensively infiltrated by organized white supremacists, and that was true even before we had an Administration that stopped bothering with dog whistles and used openly racist appeals to justify immigration policy, setting the tone for those underneath.

Not a great time to be a non-(White European) immigrant. Or even citizen of non-(White European) descent, as the casual disregard for due process in immigration related matters has seen several of them get extended stays in immigration detention despite ready ability to demonstrate citizenship.

"As someone who has never had a social media account, I have wondered if US customs would believe me if I traveled there and they asked me about it?"

In my case, I personally do not use social media, but rsync.net (a corporation in California) has, and uses, a Twitter and Github account, etc.

I am the owner of rsync.net so ... do I have social media accounts ?

Or if that's grounds for denial.

In all honesty, I’m not sure.

you can send your hackernews account maybe?

I imagine they would consider a HN account “social media”.

Depends on the colour of your skin, your class, your job, your sexuality, how you part your hair, your tattoos etc.