It's not unusual for spring flowering shrubs to carry some flowers in late summer or early autumn. One of my magnolias has had a few blooms too.

the neighbours tree has 5 flowers on it. Not at all unusual. often linked to the quality of light. same reason why some birds start nesting again, but don't go onto lay as it gets too dark too quickly.

They bloom off and on for 8 months, here. M. grandiflora isn't tied to strict seasonality, like the deciduous species are.