The two datasets (cellphone-based population flow data and Twitter data) are among the four research datasets released by the USC Big Data Health Science Center as part of the Research Data Repositories (RDR) initiative.
Check out the Twitter data description at https://bigdata.sc.edu/twitter-data/
Check out the cellphone-based population flow (ODT flow) data description at https://bigdata.sc.edu/cell-phone-based-place-visitation-data/
News release: https://bigdata.sc.edu/bdhsc-rdr-announcement/