You might as well have lectured on supersonic flight or gas turbine engines.
I'm surprised you were allowed to use that as a subject at an initial FI assessment?
Why Not?
It is giving the candidate an oportunity to show their ability to complete a lecture / briefing using the teaching and learning techniques / theory that they should have learned on the course.
The subject matter is not an issue provided that the examiner has the knowledge / background to be able to assess the candidate.
Therefore if the candidate provides an excellent lecture on particle physics including lots of appropriate mathematical equations there is noting wrong and they should be appropriately marked. Unfortunately, if the examiner hasn't got a clue about the topic then it is a tad hard to make an appropriate assessment..........but if after the lecture they have truly learned something as in the case of the Glass Cockpit lecture mentioned above one would have to say that the objectives have been acheived (at least in part).
I would find it quite disturbing to find that a candidate for the FI rating was limited to type specific and operator specific knowledge.