Yes, it was their exploratory demo called "Battleground: Infinity." But absolutely nowhere in each of those 3 links is there any mention of problems that resulted in them having to convert any system, combat mode, or any one feature at all when they were making BG.
In fact, it says
"Upon seeing the demo, [Interplay] suggested it might be a good fit for the Dungeons & Dragons license, which it had just snatched away from SSI. Infinity was recast in the world of Forgotten Realms." And then,
Virtually every RPG owes a debt to D&D, and Baldur's Gate was in some ways an effort to take the genre back to its roots, but in a very modern package.
So yes, saying that BG was initially TB but was later converted to RTwP is complete and utter nonsense. It was always RTwP.