My guess is that it was from heat and or sunlight. Maybe those sections of leaf are at an angle where they get very bright and hot maybe around noon? The same way you get sunburn on your nose before your cheeks due to it being more directly in the sun.

The straight lines look like spots that were shaded from something above. Was it very hot and bright a few days ago? Was the plant moved recently or a tree near by pruned letting more light in?

Was the plant sprayed with a soap or oil recently? Insecticide + light + heat can damage a leaf.