It does not seem unlikely to me that the group of health workers that made up most of the vaccinated group prior to April generally has a lower death rate than the unvaccinated group, which would have contained most aged 50+ at the time (vaccine uptake was <6% for the 50-59 group at the end of March).

More importantly, COVID also accounted for more than 30% of deaths in the "10-59 + Unvaccinated" group between January and April (2,761 of 8,665), as this was around the time the third wave peaked. As one would expect, this didn't really affect deaths in the vaccinated group.

I don't think anyone should attempt to draw conclusions from such a small group that is not at all representative of the whole population (in general and within the 10-59 age group).