Eh idk. The segmant you quoted says basically "if it happened once it could happen again", which really isn't a Slippery Slope Fallacy.
A Slippery Slipe Fallacy says that one thing could lead to something else which could lead to even more something else. That isn't a good argument, but to say that one thing could lead to the same thing again is a valid argument and self evident if you see that certain factors lead to that one thing, so those same factors would lead to it again.
You have never heard "on the up and up"? I thought that was like a universal saying for English speakers