I've been back and forth across the USA/Canadian border multiple times in my life, the most recent time was sometime in 2019 (I live further away from the border now, so I haven't been across in awhile). I can say I've only met ONE US border guard that wasn't an absolute power tripping cunt. So yeah. I can imagine one of them making a "joke" like that.
The Canadian guards were always professional, many of them friendly even. Thankfully, I do not see that sort of rhetoric around me where I live in the US, however, I tend to avoid MAGA morons so your millage may vary on that front.