Any Bitcoin address beginning with 1 is a P2PKH address. It is a recipe for constructing a P2PKH locking script.
That means the address is a prefix followed by a hash of a public key followed by a checksum. All that is needed here is a valid prefix, a bunch of random looking bytes and the correct checksum. So it is entirely feasible to pick a bunch of bytes that are the ASCII encoding of some sentence, pretend its a hash of a public key and just calculate the needed checksum.
It doesn’t matter that the bytes that should be a hash are not a hash of a public key because no one is ever going to construct an unlocking script using a corresponding private key.
There is no way to tell if any unspent P2PKH address is fake or real — until someone posts an unlocking script which you can check against the locking script.
By “fake” I only mean arrived at other than by constructing a private-key and public key pair in the usual way.
