Mystery coffee cup on the bus. I look for the owner and I can’t find one

So I’m sitting on the bus commuting home after work. I’m sitting in my usual spot a few rows up from the back. This is a bus that takes me across town, so it’s a long 30 minute ride that will require me to stand close to the time I get off. We’ve been driving for about 10 minutes and I notice a coffee cup on the seat across from me. I look up and down the bus and can’t see anyone that might be using it. It’s almost half full, so I’m thinking that this cup has to belong to someone. I’m looking up and down the bus staring at everyone and not one person meets my gaze. It’s as if I’m invisible. I’m looking over my shoulder, I’m checking the back of the bus, I’m getting up and checking the seats all the way up to the front. I’m looking into people's hands. I’m actually standing up from my seat and wandering up and down the bus for about 7 minutes and I can’t find anyone that might suppose to be holding that cup. Of course, 5 minutes before the bus is about to arrive at my stop it’s still sitting there. I get off the bus and start walking on my way and I feel like I’m going crazy. What just happened? Why was this cup on the bus. Did someone just somehow lose a cup??????