That is correct. A Joye Ego charger cable is a fast charger to charge the big Ego in a reasonable amount of time and it puts out 400mA or more of current. The slim 510's use a 510 charger cable that puts out around 150-220mA of current. The Ego's fast charger can damage slim 510 batteries.
And I can attest to that because TWO idiot vendors sent me what were actually Ego charging cables instead of the 510 cables I ordered and expected (one INSIDE a clone 510 kit from TW) and it took me months to figure out why my slim 510 batteries were getting hurt and not holding a charge well anymore (since they are safe from leaks as manual 510s and I never put anything too low resistance on them). I discovered one 420mah cable after I bought a good magnifying glass, then I relabeled as a Riva/Ego cable and now use it at work to charge my Riva. I bought a replacement 510 cable elsewhere and double checked the mA when I got it. I also bought 2 new 510 batteries to replace the damaged ones. Now a mere month later 2 batteries weren't holding charge right (the two new ones) and I discover my very first 510 cable from my first 510 kit with a vendor's little design on it - the one that came INSIDE a 510 kit from them - 420mA. I am steamed. I just bought 2 more cables from a reliable vendor and I will still double check them when I receive them before I use them.
Buy the correct cable - try Liberty-Flights.com. And WARNING - if what you have is FS510, they need their own cable only. That one 510 clone model is reverse polarity and will fry in a normal 510 charger and vice versa.
BTW - the USB to AC power part should be usable for any battery cable as long is it has 4.2 to 5v output and at least the mA the cable wants to output. So if the AC part only outputs 300mA, it would be fine for a 510 cable (the 510 cable will take just the mA it needs) but that AC part would not be enough for an Ego cable that wants to output 420mA. If the AC part puts out a full 500mA or more (or at least the mA the Ego cable wants to output), than either battery cable would work on it. I actually use a 4-port USB to AC that has 2000mA split between the 4 ports according to their needs, enough to charge 4 assorted batteries (Rosewill RUC6180 - see Amazon, or RUC6181 for the international model).
"ATTENTION: This kind of USB charger can't be used to charger JOYE510 batteries of it will destroy the batteries". 
My friend gave me this starter kit. And I can't remember what she told me this one is, but for wome reason i was thinking it's a 510... And now I've got this little warning that may or may not be telling me not to charge my batteries.... Can some one who's more knowledgeable please clue me in?
