I'd ascribe "deep tech" to anything that you can reasonably get a PhD in and have it not be unusual. There are dozens of academic conferences on DBs pushing the frontier forward.
The dude doesn't know anything about databases.
However, the commenter I was responding to apparently considers just about _any_ research in any significant field to be deep tech so w/e I give up and I'll go update my CV to include the phrase "deep tech research"