My apologies if you were sincere in not understanding why they made the comparison the way they did. I jumped to conclusions and assumed that you were posting in anger like so many people do here.
You're right. They weren't terribly clear on what the rationale was, but it seemed pretty obvious to me because I understood the makeup of the 13" MBP product lineup and instantly understood what they were getting at even though they didn't spell it out. A lot of people were probably similarly confused by what they did.
They actually did compare the Razer Stealth Blade to the 13" MBP. They said the Stealth Blade wins easily in part because the Blade has a dGPU and the 13" doesn't, but they also wanted to get a comparison of how both units fared with just the iGPU and with the dGPUs. Since the 13" has no dGPU, it's no possible to do that comparison with a 13" MBP, so they had to use a 15" instead and turn off the dGPU for the iGPU benchmark.
They were forthright in saying that it was not a level comparison because the 15" MBP had a size advantage, but it's not really an invalid comparison because with it's dGPU turned off, a 15" MBP is not much different from a 13" MBP in terms of performance on graphics tasks.
It wasn't done to make sure the Mac comes out on top. They were quite deferential to the Razer Blade Stealth.