I think their focus is on LGBTQ, gender equality, handouts, farmers' loan forgiveness, and weakening the military and monarchy. However, Thaksin and his sister have paid many visits to China even after they got ousted. What probably should be worried is the Harvard graduated Move Forward Party that was incarnation of Future Forward Party. That Harvard guy is a worry and might cause some troubles.
In the end of the day, China has a lot of leverages against Thailand. If new Thailand leader wanted to spoil the party then Thailand would suffer. Both high speed railway and BRICS are more beneficial to Thailand than China. China is not in a hurry to expand the high speed railway as Thailand even under the Military Junta has been dragging their feet in building the railway until Laos' high speed railway demonstrated the benefits. As for BRICS, there are many candidates that are applying so it isn't like China is the one doing the asking.