Probably an indication that Abdusattorov was playing for a win. In the main variations with 4...0-0, the theory is very developed, and it can be difficult to find an idea to unbalance the game.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... f8b4  4. d1c2 One of White's most solid options against the Nimzo-Indian.