It was definitely not his decision 100%, coaches must have talked him into it, he's a vice to vice captain only leading them because the c and vc are injured, he won't have much say in this. He was literally going strong on 367 and nothing about the way he was scoring suggested he was planning to leave that 400. The game itself wasn't even 25% complete, and with the 1st innings being 25% of the full game he didn't even need to declare until even later, ASSUMING that every other innings would also take the same amount of time (which itself didn't end up being true). So he didn't really do the team any big favour, just did the zimbabwean bowlers one by giving them a break (probably would've made some of them lose the will to play at that point)