I think in this case it's his own thought process. It goes:
If the situation was that Shen Wei was simply deeply closeted—feeling something for him but too afraid to take the first step—well, that was perfectly normal. Zhao Yunlan was rather attractive, if he said so himself. He was financially secure. He didn’t let his beastly temper show in front of just anyone, so he often gave the impression of having a great personality and being easy to talk to. With all that, he had always had good luck when it came to romance.
The whole passage is Zhao Yunlan's introspection, thinking about what is up with Shen Wei, and the "if he said so himself" reinforces that, IMO. So yeah, I'd say it's ZYL's own awareness and thinking here.
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If the situation was that Shen Wei was simply deeply closeted—feeling something for him but too afraid to take the first step—well, that was perfectly normal. Zhao Yunlan was rather attractive, if he said so himself. He was financially secure. He didn’t let his beastly temper show in front of just anyone, so he often gave the impression of having a great personality and being easy to talk to. With all that, he had always had good luck when it came to romance.
The whole passage is Zhao Yunlan's introspection, thinking about what is up with Shen Wei, and the "if he said so himself" reinforces that, IMO. So yeah, I'd say it's ZYL's own awareness and thinking here.