There is a particular context in which 慢一点 may be interpreted (functionally) to be the equivalent of 小心一点. As is often the case with languages, a lot of the nuances comes from the way the speaker and the listener interact in their dialogue, and I can see a case where this can be true.
As you know 小心一点 means to be more careful or cautious, and it is often a general expression that has a very similar meaning across most situations.
On the other hand, 慢一点 is a little bit more subject to the context, and as a general expression it just means to slow down (literally little bit slower). However, in the context where there is a sense of danger or unexpected situation encountered by someone, this can have the meaning of "Stop" (and think about what's happening).
So you can see how in this case 慢一点 can functionally be the same as 小心一点 when the intent of the speaker is for the person listening to take more care regarding the actions that they are about to undertake, or the situation that they are facing.