No species of bamboo grows in a single line. What you saw was due to pruning. Such plantings probably consisted of a number of individual plants that were kept trimmed.

Did you take any pictures that you can post here?

Thanks Kudzu. Now that I look at the pic again, I'm sure it's all down to pruning as there actually are small clumps (pic still in camera!) with just a few stems. Am going to try it myself along a fence line. Fingers crossed!

We have had luck planting "living fences". we cut the tops (about 5 or 6 feet) off fresh cut culms, planted in a shallow trench, leaving the little branches with leaves sticking up, dumped leaves on top and they are growing nicely. New plants popped up at regular interval in a strait line, very easy to do.

We chose a green clumping bamboo.
The photo is one of the plants that popped up at 4 months with no care.