Complex does not mean something that can't be understood. Like Cynefin, your uni course might also using bad definitions, if they meant those definitions for the general context. If they were giving you domain specific definitions, like in a math course or something, then your applying it to this situation might be your misunderstanding. We have dictionaries for just this purpose, so that we all agree what words mean. Words also have multiple meanings, so while it may be true that what the PEP authors said makes no sense to you, it's best if we avoid egg on our faces by calling someone else wrong if the problem is that we didn't take the time to understand what they meant, or assumed incorrectly that our understanding is the only one possible.

The common definitions of complex and complicated are that they're synonymous, there is no strong or fundamental distinction between them in the way you're trying to suggest. That's the main problem with the PEP statement. Trying to assert there's a difference is likely to result in miscommunication, this uni course and the PEP authors are both making the same mistake.

adjective 1. composed of elaborately interconnected parts; complex: complicated apparatus for measuring brain functions.

http://www.dictionary.com/browse/complicated

https://en.m.wiktionary.org/wiki/complex

https://en.m.wiktionary.org/wiki/complicated

https://www.merriam-webster.com/dictionary/complex

https://www.merriam-webster.com/dictionary/complicated

https://dictionary.cambridge.org/us/dictionary/english/compl...

https://dictionary.cambridge.org/us/dictionary/english/compl...