Not necessarily. The biological species concept is based on the criteria that populations don't interbreed in the wild. It doesn't require that distinct species are biologically incapable of hybridizing, but just that they do not in fact do so in nature (or do so with a low enough frequency that the populations still remain effectively isolated, i.e. rarely enough that it doesn't matter).
Animals like these marine mammals kept in captivity may behave very differently than in the open ocean. The article doesn't give any details. Maybe there were just one or a few false killer whales. They were apparently kept with the porpoises and therefore may have behaved as members of the porpoise herd. They may have thereby learned and adopted behaviors they wouldn't in the wild. It's likely that normal behaviors, geographical or ecological distribution, and the like, would prevent this from happening in nature.
It strikes me that hybridization supports evolution better than it supports fixed species. If hybrids are possible, it answers the question of how "new" organisms find mates.
Even difference in chromosome count is not an absolute barrier to reproduction.
Right, it is hard for creationists to focus on populations instead of individuals. Thinking in terms of populations requires more complex thought and ruins the ideas of creationism.
That is why I try to explain alleles to creationists. The largest "proof" that evolution is happening is the number of alleles in loci in various species. For instance, if Adam and Eve were the first creation of humans and humans don't evolve, there could only be a total of 4 alleles at any one loci. At some loci there are many more than that.
Creationism is debunked by this one fact.