I think the most plausible explanation for the Kiev pincer in the early days is it was a feint, which is a tactic the Soviets developed and used extensively. Its point was mainly to put pressure on the Ukraine government and prevent them from being able to commit more forces to the actual front in Donbass. If there had been no resistance, maybe they would have taken the opportunity and pushed into Kiev, but they pulled out when early negotiations were making progress.