No, this explorer is not stuck, you can easily determine this by comparing the hash values, only the genesis block is the same. This chain and the network moves as a parallel in the mainnet and has been restarted, as far as I can see.
I don't really understand the whole thing yet, but I have compiled Bitcoin Core according to this documentation, am already connected to the network and have mined 15 blocks so far, which corresponds to 750BTC or is this now an error in the matrix?