I've never gotten saltiness from coffee before, and I've been drinking my coffee black for years. I admittedly don't have the most refined palate for coffee, I tend to drink whatever preground stuff I get at the supermarket that comes in the biggest, cheapest can, but for the purposes of this question that's probably roughly the same as your office coffee, though probably a few notches below Starbuck and such.

But as I think others have noted, a tiny bit of salt is a fairly common hack to cut bitterness in coffee, so it could be that wherever your getting coffee is doing that. I've done it once or twice when I've ended up with particularly shitty coffee from my penny-pinching ways. If that's the case, they really they shouldn't be adding enough that you can taste the salt, a small pinch of salt in a pot is really all that's called for.

That said, while my coffee drinking habits leave a lot to be desired, I do have a pretty decent taste for a lot of other things, and taste tends to be very subjective, if you get a few whiskey snobs together to compare tasting notes on the same bottle, you'll probably end up with a few oddball notes that don't match everyone else's and no one's notes will ever be exactly the same, and none of them are necessarily wrong, that's what they're tasting. Genetics, what you're used to, what you ate before, what you're smelling, the cleanliness of your cup, the weather, etc. can all have an impact on how you experience your food/drink. Some people are more sensitive to certain smells and tastes than others, and I'll bet that there is almost definitely some ammount of salt and/or other similar chemicals in your coffee, maybe not to be detectable to most people, and almost definitely not enough to be significant in a dietary sense, but maybe enough to be noticeable by someone with your genetics and/or environmental factors.