After monitoring this plant since installation last June, it seems that the cultivar planted may or may not be the contracted ‘Yuki Snowflake’. Its growth habit, foliage color, and flower morphology seem to align with the Nikko type Deutzia.

The real problem comes if this is another substitution:
Mature Size & Habit
• Yuki Snowflake: 12–24" tall, 12–24" wide, compact mound
• Nikko: 18–24" tall, 36–60" wide, spreading habit

We barely have 24" to spare, before running into plants on both sides of this bush. So, a 5' wide, wrong cultivar will never be able to stay where this sits. I guess we'll know more with time.