the output shows that an import function is already present

Actually, it shows that an entry for import has been added to the symbol table.

use 5.10;
use Devel::Peek;

use foo;
say join " ", keys %{"foo::"};
Dump ${"foo::"}{import}'
__END__

# Output:

import
SV = PVGV(0x55c979ee96a0) at 0x55c979e89f30
  REFCNT = 1
  FLAGS = (MULTI)
  NAME = "import"
  NAMELEN = 6
  GvSTASH = 0x55c979ef40e0    "foo"
  FLAGS = 0x2
  GP = 0x55c979f017e0
    SV = 0x0
    REFCNT = 1
    IO = 0x0
    FORM = 0x0  
    AV = 0x0
    HV = 0x0
    CV = 0x0
    CVGEN = 0x6
    GPFLAGS = 0x0 ()
    LINE = 1
    FILE = "-e"
    EGV = 0x55c979e89f30    "import"
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You can see that the function slot is empty where it says CV = 0x0