reads from the filehandle $file (which isn't a filehandle

Yes and no. It's a string being passed to 1-arg open and readline, which are glob contexts. So it's interpreted as a symbolic glob reference (and a glob reference is the typical type of a filehandle), which makes strict complain.

But without strict, it works just fine as a filehandle:

$ perl -we'$file = "foo.bak"; ${"foo.bak"} = "seq 10|"; open $file or 
+die "nope:$!"; print for <$file>'
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