I am not an MD, but...

The time it takes for most cancers to develop far enough to be picked up by these sorts of diagnosis techniques is far, far longer than the few months which had elapsed between the Fukushima event and his diagnosis.

Is there any validity to the claim that people develop cancer independent of nuclear power plants? Absolutely. Cancer predates nuclear power by millennia.

http://fukushima-diary.com/ is where i go to get my non-officially sanctioned news about the disaster.

Sure.

On the other hand they have been caught lying and downplaying Fukushima several times.

Public statements in these kind of highly debated public/political cases also serve the role of "damage control".

Yes, there is.

If we see a wave of cancers among Fukushima workers, that would change matters, but as things stand now it seems much, much more likely that Mr Yoshida got sick for reasons that have nothing to do with the radiation.

I don't entirely discount the possibility of a cover-up, but grieving relatives who have somebody to blame are kind of hard to silence.