How do I know if the cats I've been feeding outside are feral or stray?
This is certain: if you can pet the cat, the cat is not feral.The converse is not always true. A cat that does not allow human contact is not necessarily feral. She may be feral. She may also be a frightened domesticated cat that has recently become lost. Alley Cat Allies addresses this issue on their FAQ page.
For your safety, and that of the cat, do not attempt to corner or catch a cat you believe may be stray or feral. Attempting to handle a feral cat, or any cornered animal for that matter, is extremely dangerous.