They put it on the chassis dyno and they measure the power at the wheels, then estimate what it is at the flywheel. There are ways to get a good estimation, but it is only an estimation.
The only way to know for sure exactly what it is is to measure the same engine on the same dyno at the flywheel and at the wheels. That has been done, and the figures are available. Your dyno may have simply used the "standard" power loss estimate figure of 17%. That is about right for a rear-whhel drive car with a diff that has to turn the drive 90 degrees. Four-wheel drives usually have higher losses because there's two diffs. Front wheel drives usually have a bit less. Its probably about 15%, though all those numbers depend on the gear you're in.
Assuming its 15% your car which measures out at 148 bhp on that dyno would produce about 174 bhp at the flywheel on that dyno.
But, unfortunately, you can only compare that number to other cars dynoed on that particular dyno. It'll be similar number on other dynos, but dynos do vary.