(It actually has 7 slots, but that's not important.)

Yes, it does create those methods. Each of those subroutines is a closure over $datum, so each one knows exactly what $datum it is dealing with.

As for the shift->classobj(), that shift is affecting the @_ that came into the subroutine. So, if you were to say:

my $x = $self->foo();
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where foo is some legal datum, what happens it the anonymous sub's @_ is populated with $self. That is shift'ed, then the _classobj() method is called on it and assigned to $self within the anonymous subroutine.