I'm not sure where the confusion is coming from. From the video clip & transcript:

There have been 42 deaths in England, people confirmed with the delta variant who died within 28 days of a positive test. of those, 23 were unvaccinated.

That seems pretty straight forward. Forty two people who tested positive for the delta variant died within 28 days. Twenty three of them had not been vaccinated. So, (23/42)*100 = 55% of those 42 dead victims were unvaccinated.

So far so good, but then we have a comment:

Looking closely at the wording - people who had been vaccinated but not 21 or 14 days before and had died might be included in that 55% as well.

I'm not following that. It says the 23 dead - the 55% - were not vaccinated. How is it possible to include "people who had been vaccinated" in the group that had not been vaccinated?