I don't know whether to laugh or cry. A little of both. A Samurai is not the same as a Knight, 'our' cultures were as far apart as can be. He is not theoretically bound -- he lives it, and his Honour defines Who He Is rather than What He Has.
Knights are Cowardly Scum who do not have the same Warrior Spirit and walk around in ugly buckets (Cultural racism at its' finest) they liked to call armour. Being a Samurai and being a Knight are two different things. Samurai were anything but Minor, they ruled Nihon for a very long time. And they would weep if I let you get away with saying that.

A Knight has no Soul.
(don't bite my head off for being racist, I admit it. I am defending Honour, and establishing a 'truth' that I suspect you would only call prejudice and narrow-mindedness because we look at things a bit differently)

Mutually Reasonable Discussion
The words Ninja and Shinobi, as far as I know, are more recent terms that people use to refer to them. They were called many different things, and the usage varied depending on who and where you were asking.

To deserve to be called Shinobi, you must live in the Shadows. It is more than partaking in acts of secrecy, it is living the Ninja Way. Not merely someone who partakes of secret acts, otherwise random losers and gangers would stain the Ninja Name. If there were Ninja 'Clans' (I suspect there were, being alone would be worse than death) they would not advertise it as much as insinuate it.
A Clan can grow or shrink based on adopted members, a Clan of Ninja could simply be a regular old clan headed by someone living as a Ninja, with a family of people they train as Ninja.

Saying there were no clans is silly.

A Samurai would never stain his Honour by doing something as Dishonourable as 'spying'. He would have to kill himself. He would never resort to trickery, deceit, misdirection, or Unfairness as perceived by the Universe. These words should not be seen as absolutes, they are kind of subjective.
A Samurai army could outnumber his foe's army, but he would never have them fighting with chain sickles, bombs, disguises...

I cannot explain as adequately as I would like to, so I cannot convince you as much as 'sound' like a stupid girl who thinks she knows everything.

If he wanted to keep watch on someone, he would do it openly. Or he would 'just be passing by', or 'admiring the scenery'. He would never try to be someone he was not, that kind of thing is beneath him. He is always Samurai -- a Kunoichi (ninja) can be anything she wants to be.