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"Now look at this:
SPECIFICATION: AL-ZN-MG-CU 215/ NO. 7075
We have an alloy with Zinc, Magnesium, Copper and aluminum...and of course Thickness = 3.3 mm
Isn't 3.3 mm a bit thin? And why the ingredients in the alloy?"

No according to what I am reading in the document I mentioned.
The alloyed tubing has a pretty high tensile strength as well as the fact it is a tube, so it will not bend quite so easily. The document blaster88 provides in this post, goes into all kinds of details as how intricate building such a system is. But that deviates from your question. Apparenntly this particular alloyed mix in tube form is sufficient for use in the system being discussed with the wall thickness specified. We have to remember, if it was used in the rotary parts of the unit it would have to be very light weight.
At any rate. It sure sounds like these tubes where really intended for use in centrifugal equipment and not as a rocket. Like some have indicated, why would one need such a high tensil strength tube for a small rocket that only had to travel a few miles. It would be pure waste of money.
They where waiting for sanctions to be lifted and get back into the swing of things both nuclear as well as biochemical.