Larry's right, HP is HP. His "electrician" is probably not really, and even if he is, he's wrong. It can happen...
It's a common misconception unfortunately. People, especially those not in the trade (but not exclusively) will often make bonehead assumptions like that based on some misinterpretation they partially over heard from some guy in a coffee shop or a bar. I've heard that one several times and once when I challenged an older guy on a job site who claimed to be "a 'lectrician", he got very hostile because he had been telling people this for years, fully believing it. I was accused of calling him a liar, I pointed out that he had done most of the work to that end on his own.
The other variation I hear a lot is that 3 phase motors are more efficient because single phase motors are only getting power twice per cycle rather than 3 times, or minor variations to that theme. That's not true either, in fact motor efficiency has everything to do with motor design, not the phases, and there are some sizes and designs in which 1 phase motors are actually MORE efficient than 3 phase.
HP is a shorthand expression of an amount of torque at a particular speed. There is nothing in the HP formula that refers to voltage, current, phases, weather or the price of tea in China.
The only real thing you can say is that the power delivery of a 3 phase motor is very slightly more smooth than a single phase of the same HP, because of the 3 to 2 issue. The only time anyone notices that is when you are doing some forms of high precision machining where the tiny little fluctuations in torque make tool bits cut differently or polishing equipment show striations.