Many/most people go through online exchanges to buy their bitcoin instead of meeting with people locally. These online exchanges perform KYC and will readily provide the government with which addresses you sent your bitcoin to.

Even if the government didn't have that, they might still be able to deanonymize you via your transactions. Pseudonymity is not anonymity. If a single merchant identifies you as the buyer in a transaction, the government might be able to figure out the rest of your transactions in that chain.