There's a nice guy in my neighborhood who waves and says 'hi' to me when he sees me, and I think he's a Trumpster.
He's a broad-shouldered, middle-aged white guy with a graying beard. So am I.
I think he's the groundkeeper at the Christian high school two blocks away from my house. During the summers and on weekends, I walk the track out behind the school to get a measured walk in (three and a half miles is my usual). I've been walking the track there for nearly twenty years. Over the last year, I've run in to the guy a couple of times. He'll be working, and I'll be doing my laps. Sometimes, when I come around to where he's working, he'll say 'hi' and ask me how many laps I've got left. He always smiles and is very pleasant.
He was just leaving the school in his huge black pickup truck today when he spotted me on my way to the track. He stuck his arm out of his window, waved at me, and asked "At it again?" "Yep", I replied, waved, and walked on.
He sure looks like a stereotypical Trumpster (so do I, for that matter), and as an employee of a Christian evangelical private school, if he's not a Trumpster, I will be very much surprised.
I wonder how friendly he would be with me if he knew how much I despised Trump, the evangelical church, and hell, big black pickup trucks.
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I don’t exactly hate those people myself. It's more that I'm afraid of how they might react to me when/if they find out I'm on the "other" side. They are constantly told all kinds of lies about those of us who oppose Trump: that we are all "radical" communists or socialists (or both -- they don't know the difference, of course), that we "hate this country," that we have an aversion to Trump only because we have "Trump Derangement Syndrome," and on and on. Knowing all that makes me a little more distrustful than I would be otherwise.
Whenever I have a pleasant interaction with a stranger who "seems" nice, I try to take it at face value and appreciate it for what it is. If there's a question in the back of my mind, as to whether they would be this nice to me if they knew I voted for Biden/Harris and for Harris/Walz, I try to ignore it. In some ways, I'd rather not know. If I was aware that they voted for things that I find repugnant and destructive and inhumane, I know it would affect my reaction to them, so I just choose to put on blinders and put that kind of stuff out of my mind and just respond to how they are behaving in that moment.
But I'm talking about incidents where I know I'm not likely to ever run into that person again. If I encountered someone multiple times as you described and was likely to see again, I'd definitely start wondering. I'd cautiously feel things out and try to get a sense of where they stood before getting too invested. And if I did find out for sure that they were a Trumper, I'd probably back off a little. I'd continue to be pleasant, but my guard would go up, at least a little.
I hope this guy ends up surprising you, Aristus, by turning out to be someone who is truly as nice as he seems. Who knows, maybe he took that job because it happened to be in a good location for him or because it had the kind of hours he wanted, or some other reason other than his being deeply invested in their belief system. Stranger things have happened.
For what it's worth, my husband is an old guy with gray hair and a beard, who looks like he'd be right at home at a Trump rally, but nothing could be farther from the truth. You just never know! 
black pickup trucks? 