It is Botulinum toxin, not so much the spores, that we should be concerned about when talking about food-borne botulism.
For food safety reasons, I'd recommend boiling your starter wort (and cooling it down to pitching temps) before pitching the yeast.
Regardless of storage method (refrigeration vs freezing, pressure cooked mason jars vs sanitized plastic jugs, etc.), boiling the starter wort will inactivate any botulinum toxin that may have been produced during storage. And boiling is an easy way to sanitize the flask and aluminum foil covering, as well.