Yes. This is trivially obvious by reasoning that a hash is a function that maps arbitrary data to data of a fixed size. There must be collisions otherwise it co

Yes. This is trivially obvious by reasoning that a hash is a function that maps arbitrary data to data of a fixed size. There must be collisions otherwise it couldn't hash any possible string. Usually you want a hash that maps similar strings to completely different output hashes (and I guess that's what the author actually wanted to describe). But that is not a necessity of a hash function, just a usual property.