Which means the app was crap. Rather the rules it used to validate a valid name are garbage.

Usually because someone tried to be too strict. E.g. names are space delimited A-Za-z strings, rather than just accepting any old Unicode string and safely processing it (e.g. with an SQL prepared statement).

I've had websites reject email addresses with one of the newish TLD's because someone decided they new how to validate an email address (it's more a more flexible spec than you might think).