Here is the relevant legal from Google Maps TOS:

Actual Conditions; Assumption of Risk. When you use Google Maps/Google Earth’s map data, traffic, directions, and other content, you may find that actual conditions differ from the map results and content, so exercise your independent judgment and use Google Maps/Google Earth at your own risk. You’re responsible at all times for your conduct and its consequences.

So putting the legal aside, a lot of traffic data that Google gets is from other Google Maps users or Waze users. So I only fault Google if they actually got updated data and they didn’t update the map.