Just because a few things change in plans, Todd Howard is a liar?
I would say so.
Obsidian said that Legion in New Vegas was going to have a lot of content and be on par with NCR in terms of it IIRC and they were, but Bethesda didn't extend the deadline and they were forced to cut it.
Obsidian didn't lie, they told the truth, New Vegas was gonna have more Legion content but their deadline was too short to fully design it all.
Bethesda on the other hand decides their own deadline, and Dawnguard does not seem like an expansion to me, more like a mini-expansion or a big DLC, but not an expansion.
And Hearthfire is basically like Frostcrag Spire.
So I'd say Toddy lied.