It's impossible to say. It could be one of the new varieties that blooms on new wood essentially the whole season e.g. Endless Summer, or it could be one of the older varieties that blooms on old wood. I have two varieties of the latter, All Summer's Beauty and Nikki Blue, that usually throw out blooms in the fall long after the main flush of flowers has taken place. It's not unusual at all for the old wood hydrangeas to throw out a few blooms late in the season.

I have both 'All Summer Beauty' and 'Endless Summer.' In my garden ASB has much more white in the blossoms, while ES is much richer in color. My ES is a really strong bloomer, even through light frosts in the fall. ASB is a somewhat larger shrub for me, but doesn't have nearly the bloom power most years.

All Summer Beauty (this is actually a bit paler than the reality)

Endless Summer - (also a bit bleached) pink or blue depends on pH, mine is now blue since the roots have grown into more acid soil.

My Nikko Blue's bloom in July but continue to put out blooms all fall, a few per bush.

Carol