Summary: Peter Thiel spoke at the EA Summit conferences organized in both 2013 and 2014 but was the singular keynote speaker at the 2014 conference. The other affiliation Thiel had with EA at the time was through Leverage Research and the Machine Intelligence Research Institute, two EA-affiliated non-profit organizations to which Thiel had been a major donor for multiple years. Leverage Research was one of the main organizations sponsoring the 2013 and 2014 conferences. Thiel has not donated to MIRI since at least 2015 due to a difference of perspective on the likely impact of advanced AI on the long-term future. Thiel is presently still a major donor to Leverage Research but that organization itself has not self-identified as an EA-aligned organization since at least 2018/19.
You are correct from your other comment that Peter Thiel was only one of multiple keynote speakers at the 2013 Effective Altruism Summit. He was the keynote speaker at the 2014 EA Summit.
The "EA Summits" were a series of EA conferences organized in 2013, 2014 and 2018. For the Summits in 2013 and 2014, multiple organizations were the sponsor for the event but the primary one was Leverage Research. Leverage was the only organization which organized and sponsored the EA Summit in 2018. The EA Global series of conferences was initiated as a more formal series of conferences managed by the Centre for Effective Altruism (CEA) as EA began growing more into a global movement in its own right.
From 2014 and before, Thiel's relationship to EA was through him being a repeat, major donor to both Leverage and the Machine Intelligence Research Institute (MIRI). After 2014, any direct affiliation Thiel had with EA ceased as was initiated by himself. AI alignment was the cause in EA that was the primary attraction for Thiel. He ceased donating to MIRI after he came to disagree with the relatively pessimistic perspective on the impact advanced artificial intelligence would have on the long-term future.
Thiel has continued donating to Leverage as an organization independent of EA after he otherwise ceased donating to any other EA-affiliated organizations. Leverage Research explicitly stopped self-identifying as an EA-aligned organization from 2018/19 onward. Geoff Anders, the founder and executive director of Leverage Research, is on the record as Peter Thiel still being a major, repeat donor to the organization as of 2021/22.
He also gave a talk at the EA Summit 2014