Heidegger suggested that philosophy had forgotten being; and he proposed to recover this; or at least attempt its excavation. His question: Being qua Being - what is this about? What is the Being in this proposition? It is sometimes translated as 'Being that considers his own Being as a problem'; which is also the Descartian cogito in a sense.
Being in Aristotle, is substance (ousia); and is later tied to the Christian tradition as the ground of beings (in the plural) and of Being ie God; one culminating point is Spinoza; God, however, one supposes does not ask about, query, question or interrogate His own nature (His essence is existence)
Hence one suppose, Heideggers Being is not that of Aristotle - substance modified by Aquinas.
Thus, one supposes it is not in essence a theology, in the main Christian traditions, nor off-shoots; such as Spinoza.
Being for Heidgger, then seems to return to the world (he's thrown in); but is not pure physical substance - as in Lucretious; physical atoms do not have the spiritual wherewithal to question anything; but the Lucretian tradition has atoms of anima; is this the tradition he draws on - spiritualised matter?