Most common rosemary varieties bloom in winter, in climates that are suitably mild for the plant to begin with. Any time from January through April here and often with a sporadic rebloom in mid to late summer. I would not consider a winter bloom cycle to be unique to any specific cultivar.

Blooming may not be an indicator, but seems likely 'Arp', 'Hill', or other light blue flowering colder tolerant cultivar in z7.