You can't trust what most pet stores do. Most employees don't know proper husbandry. I emphasize 'most' as there are some good ones, but they are few and far between. Heating by lamp is not always bad, but BPs don't do as well because they are a more secretive snake. A lamp isn't going to warm his hot-side hide box to 92* without creating very very hot ambient temps. I doubt your lamp is going to burn your snake (assuming it is not actually inside his enclosure), but a UTH will be better for him because he can get on the warm spot but still feel secure in his hide.

The proper setup for a ball python is to have a UTH opperating on a thermostat (do NOT scimp on the thermostat!!! UTHs will overheat and burn if not opperated with one) at one end of the enclosure. This hot-spot should be at about 90-92*. Ambient temps should be at about 80* and humidity at about 50-60%. There should be 2 identical hides - one on the hot spot and one at the cool end. This will allow your BP to properly thermoregulate.