Just mentioning its name is enough to vivify it. (You're going far beyond that and assigning a value to it!) Using a symbolic reference doesn't vivify it until the reference evaluated.

>perl -le"$pkg::var1; $pkg::{'var2'}; print for keys %pkg::;"
var1
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I'm not sure I understand your disconnect. Do you think

$pkg::var = "foo";
package pkg;
print $var;
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is different than

package pkg;
$var = "foo";
print $var;
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They're not.