well, yes, that does sound high. was it a new TL? but anyway, say for example he did hit 150 with 1 (which he didnt) then adding a second woofer would get a 153 by theory, then doubling the power to compensate for the second sub would be 156. and then adding the powere for the 3rd sub and adding the 3rd sub would be a 159. doubling power is 3db appx and doubling subs is 3db appx. doubling, not adding what you started. ex: 100->200 3db 200->300 1.5 db 300->400 1db etc.
Theoretically, if your friend hit a 144 with one dual 4 ohm Type R wired to 2 ohms, he may be hitting 150 with two by wiring both subs to 1 ohm (if the amp can handle and 1 ohm is equal to twice the wattage as 2 ohms)
Basically for every sub that you add with the same power as the other sub(s), there is an added 6 decibles.