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It doesn't really matter how much more experience he has than you: if he's asking you to testread, he presumably wants your opinion as a reader. And this case, he didn't provide enough detail for ...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/30756 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
It doesn't really matter how much more experience he has than you: if he's asking you to testread, he presumably wants your opinion as a reader. And this case, he didn't provide enough detail for you, the reader, to visualize the setting. You can't stand in for all readers, but let him know, that for _you,_ the more sketchy approach to describing that setting did _not_ work. You aren't "forcing" an opinion unless you actually have a way to make him change his writing to match your preferences. He will still make the final decisions as a writer, but there's no point having a testreader if a) that reader suppresses his or her reactions or b) the writer fights all the feedback.