Upvote for calling out the ambiguity in the title:

• “Doom popularized some mechanics still used today” - this is not that.
• “FPS engines descend from ideas in the Doom source code” - this is not that.
• “id named their engines with ‘Tech’” - this isn’t that, Doom was before that.
• “Modern descendants of the original Doom engine can informally be called ‘tech’” - this is what the title means.