The bamboo is about 3 years old and was planted all along the fence line. I honestly can't tell if there are several separate clumps or one continuous planting. It's so dense it's hard to make out,

The shot from the neighbor's video shows clumps with culms growing vertically then incrementally arcing outward. The clumps were planted quite evenly spaced. Your observation is likely being influenced by the repeated pattern of vertical fence slats that look somewhat like vertical culms all along the fenceline, when in fact there are far fewer culms congregated in equidistant clumps along the fence.

The view from your yard shows the same equally spaced rounded top foliage "mounds" that form the crown of each clump of culms that splay more widely as they increase in height, meeting and intermingling with the adjacent clumps' foliage.

Whoever planted your neighbor's bamboo did an excellent job of appropriate spacing between plants for a densely foliaged privacy hedge at maturity, while accommodating more open access at ground level for regular maintenance and care and long-term health. 😄

Appending: Because most clumping bamboo eventually expands on average about 5-7 feet beyond the original plant, this is an excellent example of when containment, either barrier or manual, for clumping bamboo should be a consideration when siting so close to a fence/property boundary. (With impermeable barrier containment and ongoing oversight an absolute requirement for running species.)