Silbaugh,
If you are using the online links (looks like you used dictionary.com instead of Websters), as your example, then let's use the entire definitions
Further down in dictionary.com, it also states poach as a verb, that among others includes the definition "to take game or fish illegally".
At the Webster's link, it also states "also: to take game or fish illegally".
Let's not cherry pick parts of the definition, let's source the entire definition if we are going to use a dictionary as our source
Just on a historical note, both mention the word's origin in middle England. That helps explain the "landowner" part, because back then, the land and the game upon it belonged to the lord who owned the lands.
Looks like both Websters and dictionary.com have included the more modern definition of the term. Even Oxford dictionary from England has updated it to include "Illegally hunt or catch (game or fish) on land that is not one's own, or in contravention of official protection." In this case, official protection would be the gamelaws.
http://www.merriam-webster.com/dictionary/poach
http://www.dictionary.com/browse/poaching
https://en.oxforddictionaries.com/definition/us/poach
And for the record, I deplore poachers of all types, both private and commercial. You see it all the time, folk with too many lobsters, too many fish, undersized fish. All because the either think the rules don't apply to them, or think that they are the exception. It is, pure and simple, a case of where there is no sense of community or tribe. Folks are out for what benefits them alone, and to heck with how it affects those to their left and their right.