He is using a regulated mod. The input controller handles the amps and send the result to the output controller which outputs the watts. Without going into a ton of math, all ohms law calculations are done by the mod, therefore amps have nothing to do with safety. Mechanical mods, yes, but not regulated. See..
http://blog.thevaporist.org/2015/12/29/regulated-mods/
Basically, the input controller pulls the required power (amps) required and passes it to the output controller. Remember, just because you have a 25A battery, doesn't mean it is actually going to use 25A. That is only for CDR which is a standard for how many amps can be used without causing the battery to overheat. Example... a 20A battery with a 0.21 ohm resistor (coil) can safely discharge from full to empty without overheating (venting) however, the same 20A battery can be used with a 0.10 ohm coil but will provide 37A (but will overheat if discharged constantly) Mech mods take advantage of this because they do not fire constantly. At 0.30 ohm resistance only 12.33A is drawn. In other words, CDR has more to do with battery chemistry than power.
The MaH of a battery is how much charge the battery holds. 3000mah vs 2500mah. More than anything, you want to look at battery quality, LG and Samsung are both quality batteries, hence either one is fine. (although the 3000mah will last longer on a single charge)