Is Aurora L1 or L2?

The definitions of these things are not crystal clear yet, but we would distinguish them as: "L2s" are networks like Arbitrum, which inherit their security from Ethereum, while "Sidechains" are networks like Aurora (and Avalanche, Fantom, BSC etc.) which do not settle their transactions on Ethereum, but are "Ethereum compatible" (i.e. EVMs), and for that reason are, like L2s, considered as "Ethereum scaling solutions".