Genetic pros or consequences of children born to parents of mixed nationalities?
Did you read the rest of that article? The authors suggest many alternative possibilities for the effects they observe:


  Several hypotheses have been postulated, including the idea that fathers with social disability potentially due to a genetic mechanism associated with autism may be less able to find a spouse from their own country and may therefore find a wife from a foreign country with whom to have children91. More likely, Gillberg et al.91 suggested that women born in another country may not be immunized against the common infectious agents in the country in which she gives birth and may therefore be more susceptible to relatively innocuous infections which may increase the risk for autism. Other possible explanations include a potential role of maternal stress due to the demands of residing in a new country, particularly with limited social support, or stress resulting from the experience of emigrating, perhaps due to economic or social factors. These hypotheses do not explain the relationship with maternal place of birth seen in a cohort study of children born in California between 1989-199416, which showed a 40% decreased risk of autism among the children of women born in Mexico as compared to California. The association between maternal immigration and autism risk requires further examination in other areas of the world to examine whether the relationship can truly be generalized.
  Gardener et al., 2009


(emphasis mine) 

In addition to these factors, note that p-value for that trend was only .06, and although there are a lot of problems with basing conclusions on fairly arbitrary p-values, a p-value of .06 suggests that differences of the magnitudes observed would often occur by chance. I'd say it's an area of open study, but it is quite a leap to jump to a conclusion that mixed nationalities result in higher incidences of things like autism from 1) the observation of a very small cohort of 12 children and 2) this other study which suggests many alternative possibilities for what is a small and possibly insignificant effect.

There are two main benefits for populations to avoid becoming inbred. The first is that there may be many deleterious alleles with low-incidence across a whole population, but you have a very high likelihood of producing a homozygous recessive offspring with a close relative. The second is overall maintenance of genetic diversity across a population, which could be important if suddenly exposed to a new disease, for example.

However, it is also possible for outbreeding depression to occur, which is a reduction in fitness after mating genetically distant individuals. However, outbreeding depression usually occurs either when fitness of some variable is low at intermediate values: for example, high fitness for small or large animals, but not for medium-sized animals, perhaps due to slightly different niches within the same species. Outbreeding depression can also occur when there is sufficient genetic separation between two individuals such that their whole protein milieu has evolved on a different background, such that alleles that cause no problems in either population alone are incompatible with alleles in the other population.

This previous answer here on Biology.SE talks about the lack of evidence for outbreeding depression in humans and a bit about why. Briefly, there is simply not the type of disparity in fitness conditions or sufficient genetic variability within humans for either of those situations to occur.