It is quite likely very true that many, if not most, Haven players multi-realm (& some even dual-log in more than one realm, alas). Years ago, right after the Horus/Raven merger, the statistics GameSamba gathered & chose to share with their GM staff & some GC's on this very topic clearly showed that to be the case (around 1/2). Like it or not tho (I don't, but it is what it is), I'd assuredly venture that in all likelihood, 3-4 years later, that even more have chosen to do so by now....
Now, all that said, if you are looking for a firm reason as to why Alsius chose to help Syrtis today, to take your one & only gem away, consider this: Ignis had just earlier this same day taken the one & only gem Alsius had, with quite the zerg on (25+ at least), when Alsius had but that one gem, yet Syrtis had 5. Call it payback, call it revenge, call it spite, call it a strategic choice to reset the gems, but imho it's best not to blame it on multi-realming, not this time ... you selfish 'pigs' brought down the thunder on yourselves.