Both the original paper and the subsequent one were published in Medical Hypothesis.
This is a journal that, by design, includes:
ideas which have a great deal of observational support and some hypotheses where experimental support is yet fragmentary [...] opening the field to radical hypotheses which would be rejected by most conventional journals.
It is an excellent source of novel ideas that may lead to experiments, but it is not a good place to find solid theories supported by substantial evidence.
In a way, it did its job, in that it inspired a more rigorous study of the evidence:
Here, the aim was to replicate the findings of those previous few studies that have suggested a reduced lifespan of individuals born during the years of high solar activity, measured as the sunspot numbers.
This author looked at a large amount of data - data from ten (mainly European) countries, over a period of over 160 years.
These data, however, provided no evidence that human
life expectancy at birth was related to solar activity during
gestation among the countries studied.
So, this was a nice idea, but was ultimately not correct.