I had something that looks almost exactly like that on my 4" tomato seedlings after spraying them with compost tea in the late afternoon, which then went in a mini greenhouse. Oops.
I set them out in the sun and sprayed with a diluted whole milk and corn starch mix. The spots did not progress much, but the affected leaves eventually yellowed and dried, so I cut them off. Was it fungal? bacterial? leaf edema? I'm not sure, but its gone (for now at least).