a strange log (no replies)

Hi,
I have a strange log from 169.229.3.91 (University of California at
Berkeley ISTDATA (NET-169-229-0-0-2) 169.229.0.0 - 169.229.255.255).
[06/May/2016:13:03:10 +0200] .... 5\xF5\x13\xED\xCA
upstream_response_time - msec 1462532590.541 request_time 0.150
Is it usual to use command char in header ?
Is this an exploit or something else ?
Best regards
Christophe

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