Since book income was less than tax income, you paid less tax in the current year than you were supposed to becauses of the temporary difference.  Next year it will reverse (meaning taxable income will increase because of the reversal), and you will owe more tax next year.  When you owe something in the future, thats a liability.

To put it this way:

A deferred tax liability is a future payable (eg, current tax depr>Book; Prepaid exp on book, installment sales used for tax or contractor acctg);

whereas, a deferred tax asset is a future receivable (e.g,Unearned rent, unearned interest (taxable income before book), Bad Debt on book and Estimated Liab/Warranty Exp (allowance for GAAP but Direct Write-off for tax)).

My goodness, FAR is super-detail-oriented.