I don't think it implies that's it's great _beacuse_ of that, just that it appears to be a single thing. Some people like to pick investments that fit their world view: the price of oil will continue to rise, I'll buy crude oil futures. You might be tempted to also buy Exxon Mobil (NYSE:XOM), thinking they are a "pure play" and they are more pure than most, I guess; but they also do chemicals and coal, among other things. So your purchase isn't exactly a "put your money where your moth is" play.
But say you were bullish on sewing machines, thinking the worldwide pent-up demand for sewing machines must be huge. You might be tempted to buy shares in Singer (NYSE:SEW)[*] ... but they aren't a pure play at all, having diversified in the 60's ... last I checked, the majority of their revenue comes from aerospace (specifically missile guidance systems; who knew?).
[*] Nevermind that they are (barely) trading below $1 and are just about to emerge from bankruptcy.
/jordan