Polygon is a sidechain. What makes people think it is a Layer 2?

Hi!

I know this question is related to Polygon but I would like to have the Ethereum community's point of view. After all, Polygon is a scalability solution for Ethereum and each one is making the other one better.

nb: It is a misuse of language but I'm talking about Polygon PoS. Polygon zkEVM is indeed a layer 2 solution, from what I understand.

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When I read about Polygon, half of the time, it is described as a Layer 2 solution. However, upon closer examination, it appears that technically, it functions as a sidechain.

I understand the distinction between Layer 2 and sidechain at a high level: Layer 2 security relies on Ethereum, whereas a sidechain is a completely independant chain that manages its own security with its own set of validators and consensus.

Though, I don´t really understand:

• what makes people think Polygon is a Layer 2. I also could ask "What part of Polygon architecture follows the Layer 2 pattern?" ;
• what makes actually Polygon a sidechain. I also could ask "What part of Polygon architecture follows the sidechain pattern?".

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I hope my questions are clear.

Thank your for reading and sharing your thoughts / explanations!

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EDIT: I precised that I'm referring to Polygon PoS