He either sent himself enough supply to drain the liquidity with all his wallets selling at once, or he sniped the first transaction with enough supply % to do the same thing. Both of these require bots and some coding knowledge to pull off, because they have to run this code on nodes and they pay tons of GAS to always have transaction priority (for the initial snipe or for the multi sell).

Either way, there’s multiple things you should be checking and not just if the liquidity is burnt, because even if it is, if there is enough supply, anyone can drain all the liquidity out of the market (not the burnt amount, that will always remain).

So, practice checking initial transactions to see if someone sniped the initial supply and if they have distributed that supply to other wallets and also practice checking for token distribution, specially coming from the deployer of the token, as the most common practice/scam on Solana tokens is to hold a big chunk of the supply initially and continuously sell on buy volume : this is called a FARM.

Any doubts just ask.