we all know, Perl support same name but different type, that means $foo and @foo could be both exist without any violation.

It is singular, plural and named items. Remeber, perl was invented by a linguist. Identifiers are stems from which substantives (singular and plural) and verbs can be derived, etc.

Same as in English e.g. "cow" and "cows" where $cow is one cow and @cow is a herd, %cow are the pet cows callable by name. Well, $cow could contain a cat, @cow could contain a gang of bulls and %cow the members of the cowboy family, but that's meant as freedom for the programmer to introduce bugs.