Poaching has always had a certain connotation that you snatched/stole/etc. someone from another employer. Of course, we use "steal" in other contexts where it's perfectly legal/by the rules: steal second base, this thing I bought was a steal, etc. So there's a long history of using this language in English for things that aren't actually illegal or underhanded.

That said, I understand why people object to it and it may be one of those terms it's better to avoid even if it's used playfully.