"Poaching" is often the word of the sore loser.
In experience, the benign recommendation of people you like working with, and the reachout of the current company's HR is the lightest of all possible recruitment efforts. After all, your coworker didn't even have to tell you no. And if you were peers, there's no case of former-boss pressure, either.
The times I see the most defensiveness on this score is when a major manager or executive leaves, and a huge chunk of the work force follows along. Most people find bosses they love, and when a big boss leaves, there's both a morale issue, and a desire (if the boss is good) to follow the good leader. The old company knows this, and may put serious pressure on the outgoing boss to avoid "poaching". How that breaks down is a largely case by case situation.
From a peer to peer level, if you were actively recruiting your old coworkers - taking them out for drinks, convincing them to apply and then reaping a reward - you might want to watch the pressure of your sales tactics. But if you're just recommending a good person for a good opportunity, you don't have to be afraid of in a rational situation.
NOTE: I say "rational" - there's all sorts of drama and ill-will in this area of the work place. Having employees quit your company or group is never fun as management, and I've heard plenty of tales of fairly insane responses to this event. So... while I'd like to think the majority of former companies will realize that this happens, you can end up with the irrational case pretty easily with the right adverse conditions adding to the mix.