Replacing Bontrager Race Lite Freehub
It's hard to know exactly why that cap is so well stuck on, but you are right, it should pop of with a good firm tug. I believe there is a rubber O-ring that keeps it on. I have a DT-Swiss wheel that uses a similar cap, and when mine was stuck on like this,
soapy water helped me. I diluted some dish soap and poured a tad all around the cap and it popped right off. If you have an axle vise or a large drill chuck that might help you grab onto that thing to give it a good pull.