What is it with Chinese robots anyway? They always seem to put on UA strings that would get them blocked even from a previously unknown IP.
Personal hunch: the idea is to lull servers into complacency by first asking for robots.txt. It isn't very determined though; it goes away after one or two 403s. (If anyone has been asleep for the last five years, the uber-range is 18.104.22.168/10. If only Ukrainian robots lived in such nice fat /10 blocks!)
Cursory log search tells me they also show up at 22.214.171.124** with the same behavior pattern except that they don't change UAs after getting robots.txt. I don't know if either one is legit; free lookup is uninformative on both.
* The referenced page is in Chinese except for the recurring phrases "sogou spider" and "robots.txt". Rumor has it they're compliant, but who gives a ###. ** Not to be confused with 126.96.36.199, which sometimes claims to be Baidu.