Perhaps your son has allergies to foods with acids? Both orange juice and spicy foods have lots of acid content. You could trial him out on the over the counter Zantac, which is an H2 blocker, and will help with allergic reactions as well as indigestion. Or his own production of gastric acids are in excess and with the added acids in those foods, it leads to sweats, like when people eat hot chilli or hot wings. If that's the case then a PPI (proton pump inhibitor) will help reduce the acid by not allowing so much to be produced. The one's that are available over the counter are Prevacid (generic version is called lansoprazole), Protonix ( can't recall generic name at the moment), or Prilosec ( generic name is Omeprazole). Good luck!
Some people do start to sweat after eating and drinking some types of foods, some may start to sneeze.
My advice is, regardless why it happens, is for him to avoid those foods if he does not want to sweat.
There are other liquids than he can drink and water is the best for us to quench our thirst. He can eat other types of fruit to get his Vitamin C and fibre.
Orange juice is fine in small quantities, but it provides no fibre and with it being acidic, this will also soften the enamel on his teeth and can cause dental decay. Get him to drink milk instead which is better for him and will help him to grow strong and healthy teeth and bones.