You can buy loan less than the minLoanSize specified in the pool in the buyLoan function of Lender contract.
There is a minimum limit to which you can buy a loan from a pool which is set as pool.minLoanSize. But while buying loan from the auction, there is no check for this case.
The pool.minLoanSize is set in the first place to prevent griefing as mentioned in the Structs.sol for struct Pool.
Manual Analysis
Add the following check if (totalDebt < pools[poolId].minLoanSize) revert LoanTooSmall(); after the line:
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