What should I check before reading too much into this night photo?

Start with the image, not the story around it. Keep the original file and compare it with the photos taken just before and after. Low light, reflections in glass, motion blur, and something close to the lens can all make ordinary shapes look strange. Cropping or brightening can help you inspect it, but try not to treat a vague shape as proof of anything by itself.

For the sounds, stay inside and check the doors are secured. If your cameras recorded the area, review the footage around the same time as the photo and see whether anything clear shows up. If you still feel uneasy, ask someone you trust to check the yard with you in daylight rather than going out alone at night.

I'd keep the possibilities open for now. A photo and a few unexplained noises don't tell you what caused them. Note the time, where you were, and what you heard, then see if there is a pattern or anything on the camera footage. If nothing turns up, that still may not settle it, but it gives you more to go on than the feeling the picture creates.