I love this sentence! We have dotykać taking the genative so we have (pomidora). But where I live in Małopolska everyone uses dotykać in the accusative. So then we should have 'Chłopiec dotyka pomidor', right? But locally they also animate masculine vegetables, so we get "Chłopiec dotyka pomidora". A sentence that is grammatically accepted in Krakow and Warsaw but for two different reasons. Did I get that all right?
If I were to provide a very simple explanation, I would probably phrase it the same way you did, but let's go a bit into detail, shall we? :)
Of course, dotykać się always works if two (or more) of something are actively touching each other, or someone is touching themselves. But in colloquial speech, this distinction vanishes. The Polish wiktionary somehow states that dotykać się is not a colloquial version of dotykać, but an emphatic form (forma wzmocniona). I believe that it can be both.
Btw, in Russian, no matter what you are touching, you are always touching yourself (касаешься) :)