OK, I live in a two-story duplex. Upper unit has the same floorplan and I live in the lower unit. The tenants upstairs flushed their toilet, and I heard what sounded like a burst of air or something shoot out of my toilet. I went in the bathroom and there was a little water splashed, but it is not like a ton of water shot out of there. That's why I think it was more of an air bubble.

What the heck was this? Should I be more concerned? Thanks.

This is what you first floor units have to contend to when you have a partial blockage downstream from your toilet and the upstairs unit flushes. Let me explain what just happened. There's a partial clog downstream from your toilet in the common main. The upstairs unit flushes and the discharge picks up speed dropping down to your level where it hits the clog and bounces back sending a bubble of sewer gas ahead of it. N That's the water shooting out of your toilet.
The solution would be to snake the drain line downstream from your toilet. You shouldn't have to bear the entire cost. If this is a condo then the problem is in a common area and the Condo Association eats the bill.
If the units are owned separately then the two units should split the bill. Good luck, Tomk