Vanke and Xin are both in the same business, building residential housing in China. Vanke is larger and focuses more on first tier cities, but they are otherwise comparable. In particular, they operate under the same rules and same macroeconomic forces. Anything good or bad one can say about real estate in China applies to both. Vanke sells for 9.5 times earnings, while XIN sells for 2.2 times earnings. This only makes sense if Vanke has over four times the growth potential of XIN, which is crazy. Similarly, Vanke sells for 1.8 times book value, while XIN sells for 0.43 times book value. Again, this only makes sense if Vanke will grow over 400% faster than XIN. Similar analysis applies to dividend yield. Like the seekingalpha article said, XIN needs to more than triple in price to $15 a share to have fair value compared to its closest rivals.
Comparing p/e ratios between XIN and other chinese real estate developers trading in Hong Kong or China isn't entirely accurate since they use different accounting methods to recognize revnue. XIN uses the percentage of completion method. So they recognized revenue as construction is being completed. The developers trading in China and Hong Kong use the delivery method which recognizes revenue when there are presales and sales of units.
To make PE roughly comparable, you can use todays market price and earnings from a year or two ago (since almost all partly completed units then will have been sold by now). By that measure XIN has a PE around 4, still less than half of Vanke's PE. XIN also has 1/4 the price to book and 3 times the dividend yield. There does not exist any fundamental measure that says XIN shouldn't at least double in price to be comparable to its immediate peers.