Okay, you need to recognize that there are greater and lesser contradictions. Yes, all property is theft, but is that a useful line for Palestinians to struggle against? Can they even meaningfully abolish property without solving the colonial question?
That's why we say the colonial question is the primary contradiction. Israelis are colonial invaders that have come to steal the land and expel or kill the indigenous population. This is a greater concern than, say, Palestinian business owners owning property (and thus stealing the land from the Commons). If we don't focus our struggles and identify the primary contradiction, we just lash out at every injustice all at once and accomplish nothing because we are overwhelmed.
Every successful decolonial struggle for national independence involves cooperation between the landless and the landed, because colonialism takes primacy. We can deal with the question of "who gets to own the land" once the invaders are gone.