There are a variety of non-destructive inspection and testing methods for composite, like ultrasonic c-scans and pulsed thermography that I know of.

And you can produce reliable composite parts (you don't want homogenous, but them to come out exactly as spec'ed) under strict control, but it doesn't look like they necessarily did that here. They seem to have eg foregone autoclave curing of the tube section probably due to cost.