Reports said omicron was found in wastewater samples several weeks ago in Disney World...so that kind of tells you it was already circulating here for a while. It was apparently enough that they assumed there was already significant community spread.
The people that are going to get tested and count as positive cases are usually people that are going to have pretty bad symptoms. If you just have a runny nose, chances are you won't go to get tested. So 150k "positive" cases a day probably translates into millions.