"Like has HIV virus known to show such phenomenon with some totally different virus?"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3324781/
"The process of recombination that takes place in RNA viruses corresponds to the formation of chimeric molecules from parental genomes of mixed origin. This process can occur either within a single genomic segment (in which case, it is often referred to as RNA recombination) or, for those viruses that possess segmented genomes, as exchange of entire genomic segments between viruses (
FIG. 1). This exchange is usually termed reassortment. Although RNA recombination and reassortment are mechanistically very different, both require that two or more viruses infect the same host cell. "
You're right that it seems very rare but it does occur naturally (non-homologous recombination):
"findings suggest that the gene was most probably obtained fortuitously by coronavirus and was not an original part ofthe viral genome. The most likely
explanation is that this gene resulted from recombination between coronavirus and influenza C virus (67). Since there is no apparent sequence homology, aside from the HE sequence, between coronavirus and influenza C virus, the acquisition of this gene by coronavirus from influenza C virus, or vice versa, could represent nonhomologous recom- bination. The homology of the HE gene between coronavi- rus and influenza C virus was obvious only at the amino acid level, but not at the nucleotide level (67); therefore, recom- bination probably occurred between their ancestral viruses. So why do some coronaviruses lack this gene? Deletion by virtue of intramolecular recombination is a plausible expla- nation, since coronavirus genes are flanked by homologous intergenic sequences (58). An alternative possibility is that the putative recombination between coronaviruses and in- fluenza C virus occurred after speciation of coronaviruses; the divergence of the HE gene then may have occurred rapidly since this is a nonessential gene. "
Also, in theory at least, the HIV or coronavirus don't necessarily need to splice directly into each other.
One of them may have infected a host animal cell and then inserted its genome, and that infected cell itself could have been exposed to the other virus, integrating parts of its genome at that exact point in disease evolution, causing the hybrid form to be replicated. This is just my speculation though.
Overall, it's unusual but seems more plausible as a natural evolutionary event than artificial.
