How did they generate these vanity addresses with 27 predetermined characters? A while ago, I read some news about a huge transaction on the Bitcoin blockchain. The first few addresses used were apparently created with some kind of vanity address generator. One example is 1Lets1xxxxxx1use1xxxxxxxxxxxy2EaMkJ.
However I recalled, when reading up on the topic a couple of years ago, that this process is very computation hungry, since it entails a brute force search for private/public keypairs. Finding a keypair with only a few predetermined public key characters would take a long time. And indeed, the Vanitygen article on the Bitcoin wiki seems to agree - finding a keypair with 12 determined public key characters would take 11,700,000 years...
So, how did they manage to generate the public key above with 27 non-random characters?
(They say that the task of finding a private key for a specific public key is futile, but extrapolating here makes you kind of wonder...)
Your observation is correct and indeed those addresses cannot be generated by vanity address generator in a reasonable amount of time.
Most likely, there is no secret key corresponding to that address and the person chose the p2pkh(and thereby the address) directly. Indeed, by looking at the explorer, there seem to be no outgoing transactions from that address.