When I first read the tread title, my thought was "we are supposed to be impressed by that?", but watching the last 300 of a few 1500s from the last few years, 40.63 is a bit more impressive of a close than I first figured ... while still not being ground-breaking.
3:33 is slow for the likes of Souleiman, so as has already been pointed out, I'd imagine there are quite a few guys out there who could close the same or faster off of 2:52 at 1200m (including Souleiman himself, if he was really challenged).
Kiplagat ran a 39.23 to edge out Kiprop in Doha in 2012 ... in a winning time of 3:29.63.
In Paris just this year Kiplagat had a 39.44 close to win in 3:30.13.
For Souleiman, I remembered him closing crazy-fast at the Continental Cup last year (albeit in a jog-fest). Looking back, he did 36.8 there (3:48.92) to nip Kiprop.
Paris 2013, Souleiman won in 3:32.55, with maybe a 41.5 last 300 (hard to be exact, as the rabbit had a gap, so official split is misleading), so this could indicate he has improved quite a bit to this year. That race though, he was 1:51 (54/57) at 800 ... clearly tying up off too fast early pace. Today's race, going about 55/58/59, was better set up to kick in.
Also of interest ... apparently Souleiman plans to double in Beijing ... according to the commentator.