2 x-rays 2 different results

My 4 year old has been sick with a cold and cough since Monday. Monday I took him in to the doctor, they said upper respiratory infection. They gave him allergy meds and said he should feel better soon. Wed I took him back to the local clinic/hospital. The RN ordered a chest X-ray. She said that he has pneumonia and also the arteries around his heart look a little enlarged. She gave him antibiotics and sent us home. I was crying my eyes out and she couldn’t give me any answers as to why?All she said was the radiologist pointed it out and it’s something that needs to be looked into. Also his blood pressure was a little on the high side.