Everyone started at zero hearts when the switch to Discourse was made. The only way the old forum's "karma" count was migrated was by granting those "Karma: n+" badges. That applied to all forum users.
Yeah, but it is not really about badges. It is about "trust level":
It is true that there is a badge for each trust level, but the badge itself is only a cosmetic symbol of your trust level. It's like a military medal: anyone might slap one on their jacket, but the privileges associated with the medal are granted by a service record, not by a bit of tin.