Yup! Have tried this in 5.10.1 and now see the difference.

use strict;
use warnings;
use 5.010;

my @arr = (2, 5 , "aaa");

say "\@arr ~~ 5 matches" if @arr ~~ 5;
say "5 ~~ \@arr matches" if 5 ~~ @arr;
say "\@arr ~~ 3 matches" if @arr ~~ 3;
__END__
5 ~~ @arr matches
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But after reading "Smart matching in detail" from perlsyn I have the impression that @arr ~~ 3 expression falls under

    Any  Num   numeric equality  $a == $b
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rule, so it should be equal to @arr == 3, and it's not, so what rule is actually applied in this case? And BTW is there any way to see what comparison have been actually performed?