Answer The Public obtains keyword monthly search volume information from various sources, including partnerships with different data providers. These sources gather data from user search behavior and provide estimates of the monthly search volume for specific keywords.
Please observe that all search volume estimations are from the previous month. I.e. If you check the keyword report in January, the search volume data is from December.
For more information on AnswerThePublic data sources, please check What Timeframe Is Your Data From? And Where do we get Cost-Per-Click from?