You actually throw the "Error" constructor here. Not an error object, just the function that could create an error.

Not that it matters much in a kata, but throwing strings instead of errors means that you won't get a stacktrace, making errors harder to locate. Don't try that at home, kids! :)

it prints "Hello Austin, welcome to PHP!", it doesn't return it

The first point in "[1.3..7]" is supposed to be a comma, right?

Wouldn't it be possible to extend the system so the kata creator defines a fixed interface? That way, test cases and code could run in two seperate runtimes.

Most katas I have seen say something like:
"define a function bla that returns a value blub"

At least this sounds more reliable then a "Cheat detection". (I could see this go horribly wrong)
Or how about allowing downvotes?

A solution that does not contain any spoilers! Nice.

\w matches numbers, letters AND underscores.