[yourface]

assuming SB isn't bad enough to not c/r the flop here with a good hand (most of the time at least), the 5 must have improved his hand

if the 5 improves his hand, he would have to have made 2pair with the 5 or have picked up a draw on the turn

unless he is getting way out of line here the only made hand he can reasonably have that would play this way is J5s, maybe 45s with Q5s being very unlikely

as for draws he can likely have any NFD and also combo draws like 9Tcc

so yah I call down here