I'm not saying it's not sunburn, it most certainly could be, but it
could also be a the result of a fungus on the Tomato leaves. Last year we had some plants which exhibited a very similar problem which didn't look like your typical early/late blight. The affected areas died back to a light brown dry, papery texture like the one in your picture.
Tell your father to water the soil, not the plant, and that Tomatoes only need a good soaking weekly even in hot weather. Keep a keen eye on some of those spots: if they grow in size nip off all the affected leaves and consider spraying the remaining good foliage with copper sulfate solution or whatever organic spray you have at your disposal; or if the whole plant is affected pull the whole thing up. You can
compost the affected parts, but do so under a layer of other material.
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Written from Xardín do Cernunnos, a little valley permaculture homestead in the beautiful hills of Galicia.