I'm trying to transfer data from one device to another using NFC. I'm trying to figure out if this is possible, I downloaded apple's sample project about CoreNFC, I was able to read NFC Tags (it wasn't a real NFC Tag, rather it was an NFC Tag emulated with an android device). Can I use my iPhone to emulate an NFC Tag to transfer data to another iPhone or Android device?
No, at least not up to this point.
Only Wallet/PassKit/Apple Pay have a way to do Host Card Emulation as of now.
There's not an API for third party developers to do HCE.