This date was revealed thanks to a free upgrade kit for MSI's all-in-one CoreLiquid R and Core Liquid K coolers that will support the new, larger socket Alder Lake's CPUs use.
Alder Lake uses the new LGA1700 socket for its chip, and while it has felt like Intel has switched sockets a bit too easily in the past, for once this feels justified—Alder Lake supports DDR5 and PCIe 5.0, and that support needs to be plumbed in somewhere.
Videocardz goes on to suggest that the full Alder Lake announcement will happen the week before on October 27 and that preorders will also be accepted on that date. With the sales and reviews of Alder Lake, aka Intel's 12th-gen desktop CPUs, happening on November 4.
The date coincides with Intel's Innovation event on October 27–28, which is a good place to launch something, even if it as a virtual show.
So far there has been no rumours about the new Z690 motherboards or DDR5 memory kits which will need changes to handle Alder Lake.
Benchmarks show that the chip will give equivalent AMD chips a run for their money, although by the time the chips start to make their mark there is a good chance that AMD will be onto another generation with Zen 4.