A simple test of his assumption should be enough to convince:

foo.pm:

  package foo;
  BEGIN { print "foo's BEGIN\n"; }
  print "foo's body\n";
  sub import {
    shift @_;
    print "foo's import: @_\n";
  }
  1;
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bar.pm:

  package bar;
  use foo qw(from bar);
  1;
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test.pl:

  use lib '.';
  use foo qw(from test.pl);
  use foo qw(from test.pl again);
  use bar;
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Output:

  $ perl test.pl
  foo's BEGIN
  foo's body
  foo's import: from test.pl
  foo's import: from test.pl again
  foo's import: from bar
  $
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BEGIN blocks are executed at compilation. use and require don't compile the same code twice.

Look in perlvar under %INC for more info:

The "require" operator uses this hash to determine whether a particular file has already been included.

blokhead