It's because of the way you have worded it, especially using the words "make everything faster" and the bit that follows the "if".
"It's the other way around. An ssd makes everything faster if you have enough memory."
An SSD will not make "everything" faster and the things that it will make faster do not always depend on how much memory you have.
An SSD will not make a CPU or GPU intensive task faster, regardless of whether you have enough RAM, or not.
An SSD will make all file operations faster, regardless of whether you have enough RAM.
Even if you don't have a lot of RAM, an SSD will make your system faster, in comparison to the same system with a HDD, because swapping in and out of memory to the disk will be faster, even though the fastest PCIe "flash" drives are still at least 10 times slower than the typical memory we have in our Macs.
...and so forth and so forth.
Do you see now?