Because that's not what matched on when it searched for qr/CSV/ on the entire list of loaded "file" names. When you (string?) eval something it stubs in a representation of the location of the eval call and its showing you just the text that got eval'd there.

And again @INC and its ordering doesn't have anything to do with the order keys returns things for the %main:: stash ( a hash, but it's a special hash). If you have %foo = qw( 2 a 22 b 222 c ) then you similarly can't say what (grep /2/, keys %h)[0] is going to wind up returning.