It normally blooms in spring but plants can re-bloom, needless to say. Alternatively, it may be this year's seedings that bloomed recently. I think you'd be hard-pressed to find any Euphorbia species that lacks the little "collars". Why don't you show a close-up of the flowers? Perhaps they are actually the seeds, which would explain why the "collars" are lacking.
Everything about it fits in terms of appearance and your description, including how it's filled that bed.
