They've got the R-73 IR guided missiles, and they're probably also trained 'already' to use them. They're not rookie pilots, plus most completed conversion in Russia before deliveries. Also they've just conducted the first trials with some of the air to surface missiles/guided munitions. ATC had the position, the Flanker has got good IRST, so there's no need to use the radar. Protocol requires visual ID anyway. But who says none were scrambled?
Looking at the S-3 and its mission/systems, looks an accident to me. Otherwise you'd have a 'P-3' on antidrug mission, while it would actually be a EP-3... also that island La Orchila is nothing of any significance as far as I know...
No follow ups it appears, so Venezuela accepted the US explanation. Don't forget that the war on drugs is also on Chavez agenda.