Ok firstly, the fact that they are in there for only a few days is realy important as it means that neither of the two species get a chance to settle down so they occupy themselves with that rather than chasing each other.
Next is the fact that I doubt the sharks in there are mature (because they'd be piled up on top of each other in a 10 gallon otherwise) seeing as they get to 6" and those usualy being sold are about 2-3". They get more aggressive as they mature, usualy at around 4-5", so at a younger age they wouldn't be much of a threat if kept temporarily with the tiger barbs.
Thirdly, tiger barbs are very quick and quite aggressive in their own right. Well maybe 'nippy' is a better way of describing it but, still, with young sharks, they can still hold their own for a while. In fact, tiger barbs kept with young sharks may cause mroe harm to the sharks than the sharks cause to them.
Lastly, with several sharks in the tank, they would be more concerned with each other than with their tankmates. Obviously, as they aren't yet mature fish, they won't be too aggressive (though they still will be to an extent) so all their attacks shouldn't cause too much damage. The fact that there are several also means any aggression is distributed quite evenly and no single shark is targeted (which would happen if there were only 2 for example and the dominant would bully the inferior to death).
Having said that, they probably still have some casualties. Though you won't necessarily have seen the bodies.
Anyway, neither the sharks nor the tiger barbs should be kept in a 10 gallon for any length of time. The shark gets too large and is too territorial, the barbs get to 2.5", should be in a school of at least 7, are nippy and are very active. Besides the disposition problems, you need to consider physical space and the fact that tiger barbs, especialy, don't appreciate fluctuations in water quality and can easily get stressed and die if exposed to this sort of situation - something which happens to be inevitable in an over-stocked tank like one with a rainbow shark and 7 tiger barbs would be. Keeping the barbs in a group less than 7 to fit them in also doesn't work because, besides that the shark will eventualy kill them, they can nip the shark and end up killing it indirectly as a result of secondary infection combined with extreme stress.
You can combine these two species in a 30 gallon or larger (which I have done but not with a rainbow shark - I had an RTBS) but in anything less you run a serious risk and in a 10 gallon it's impossible.