CBO explains their scoring….

Like all of CBO’s cost estimates, our estimate for this legislation shows the effects of the legislation relative to current law at the time we did the estimate.
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This legislation will prevent those changes in law from occurring or reduce their scope; hence, relative to what would have happened without the legislation, it embodies substantial tax cuts. The legislation also will boost deficits by increasing spending, mostly for refundable tax credits and unemployment compensation.
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f we added the estimated cost of the legislation and the related debt service to our previous baseline budget projections (which followed current law at the time), we would show additional deficits between 2013 and 2022 of roughly $4.6 trillion.

They also go on to explain the scoring used by CAP. Both are legitimate ways to look at it but the CBO’s method is different.