The Quaker hour of silence or ‘worship’ is a collective work of silence, not just an individual experience. This is probably the major difference between the Quaker contemplative tradition, as a collective practice, vs. Buddhist practice, which is predominantly a solitary, individual practice, even when practiced with a group. The orientation of Quaker contemplation is towards the collective silence, the speaking that comes out of that collective silence, and the listening that comes out of that collective silence, that we are there in Meeting to listen to each other. We listen to the silence that is collectively produced, and we process what is spoken from the silence in a collective process of discernment. And that is vastly different from singular Buddhist practice.
That said, there are also many similarities between Quaker silent contemplation and meditation—whether Buddhist, secular mindfulness, Yoga, TM or other forms of meditation. People who practice Buddhist or other forms of meditation would feel completely comfortable siting in silence in a Quaker meeting, so long as they also understood the centrality of listening to the collective silence/voice.
This video produced by Quaker Journal looks at the similarities and differences between Quaker contemplation and meditation