If the topic is not natively impossible to understand, but the speaker is choosing overly-complex words, consider "sesquipedalian". ("Sesquipedalian" has a negative connotation.)
Sesquipedalian can also be used to describe someone or something that overuses big words, like a philosophy professor or a chemistry textbook. If someone gives a sesquipedalian speech, people often assume it was smart, even if they don’t really know what it was about because they can’t understand the words. Each of those long words is referred to as a sesquipedalia.
If you feel like this choice of overly-complex words is more a product of their education and scholarly background and less a product of their ego, you may use 'erudite', although this doesn't necessarily imply that the lecture was difficult to follow. I believe that 'erudite' is neutral-positive in connotation.
having or showing knowledge that is learned by studying
If you think that the topic material itself is the primary source for their use of jargon, then you can just call it 'technical'. The following sources refer to this exact type of material as 'technical', and they appear to be using the word 'technical' to describe what you are describing.
blog post about how you should 'clarify' instead of 'dumbing down' technical details
different blog post about how to explain 'technical' things to non-technical people