Yeah, it sounds sleazy. But even if the competitor wouldn't have gotten the insider tip from that other VC, what would have prevented dozens of competitors from copying that business model after the original company had launched? If that business really takes only a few months to get it going, it probably has a very low cost of entry which is not a significant hurdle to competitors.
Yes, being the first to market gives you a slight advantage, but not so much that it can assure your success if your competitors manage to offer a better product a few months later. MySpace preceded Facebook, but look where they are now.
It is simply, "my competitor invested in X, I didn't get into the deal (or couldn't on my terms), I'm going to find something similar to X and invest in them or just launch it within my own network and fund it".