Yep, can be an allergy thing or he could be developing the start of some sort of infection. Anything that has irritated their eyes will cause that (I spilled some hot sauce on my kitchen floor and had a cat walk through while I was cleaning it up. He cleaned his face with that paw later and ended up looking a lot like your guy).
The only way to know for certain is to have the vet check it out. Who knows, he may be perfectly fine again by morning or he may be showing other signs of illness/irritation. Either way, I don't think it's anything to stress over too much tonight. He'll survive until tomorrow.