It should be obvious. Maybe you are autistic? (Autistic folk often have sensory processing issues).

Sexual attraction isn't just about looks, its about the dynamic, the flow of energy that is created when interacting with another person.

In my view, your question is like asking "how do I tell the difference between thinking a food dish is pretty and being hungry?" That's just two obviously separate things. Just because someone seems photogenic doesn't mean I'm attracted to them, just because someone is "ugly" doesn't mean I'm not going to be attracted to them. In the similar way that just because food looks like slop doesn't mean I won't get hungry looking at it.