Emulators are not necessarily bound by the same limitations as hardware so there are often mismatches between what they and their cheat engines can do vs what happens on real hardware, this being one of the major scenarios along with editing things in the video aspects.
I will have to look up what that cheat does but speed changes tend to happen for one of three reasons.
1) The machine is overclocked. Variously relevant and not for the PSP (it having a variable clock mean a lot of games use a separate thing to measure time and thus higher clocks mostly mean better framerates + lower battery life and heat compared to older machines where speeding it up means speed up everything).
It could also be a hardware thing if you are trying it on a 1000 but the cheat only works for 2000 on up or something (there are a few things that make use of the more RAM and whatnot of the 2000 on up line).
2) Some kind of disabling internal limits. Rare to see and usually considered very crude.
3) Something more internal still. If walking is slow then making the walking animation itself speed up but everything else remain the same is one way of doing things, far more of an active cheat than the things noted above. Exception being if the game has some kind of of its own internal speed up command (for cut scenes the user has already seen for instance, replays, animation disable modes, text speed being set beyond what the internal speeds might normally allow or hidden instant mode for some kind of internal purposes).
Being a 1 line cheat means it is unlikely to be 3) or if it is then it is one of the simpler ones, which is odd as those should work in hardware.
