If your biggest competition is an un- or under-funded, not yet widely known or used startup, you've got bigger problems than that startup. I find it amazing that startups will consider other startups their main competition, when the reality is both startups need to focus on the larger untapped market rather than think that each other is stealing each other's non-existent business.
Another way to put it: If the market is really that small that one small startup can take away business from another small startup, then you don't have much of a market at all, and you should find a larger market.
Anyone who goes to such extents to snipe a startup really doesn't understand what it takes to gain market traction.
But it sounds like in this case, one startup wasn't really looking to snipe another startup, but rather capitalize on the press that would (potentially) be generated from that startup's launch. This happens all the time in other industries. Whenever Apple launches a product a myriad of other companies piggy-back on the press Apple generates. It's smart marketing.
It would only be underhanded if the startup was making false or disparaging claims about the other company in public. And that's borderline libel / slander anyways.