A test file that illustrates the use of $BASH_SOURCE and $FUNCNAME

bash_source_test.sh

#!/bin/bash

function f1() {
  echo 'In f1'
  echo ''
  echo ${BASH_SOURCE[0]} + ${FUNCNAME[0]}
  echo ${BASH_SOURCE[1]} + ${FUNCNAME[1]}
}

echo 'in bash_source_test.sh'
echo ''
echo ${BASH_SOURCE[0]} + ${FUNCNAME[0]}
echo ''

execute_test

mpdaugherty@grit ~ $ ./bash_source_test.sh
in bash_source_test.sh

./bash_source_test.sh +

In f1

./bash_source_test.sh + f1
./bash_source_test.sh + main

source_test

mpdaugherty@grit ~ $ source bash_source_test.sh
in bash_source_test.sh

bash_source_test.sh +

In f1

bash_source_test.sh + f1
bash_source_test.sh + source

I needed to add a call to f1 as the last line of the script to get the same result as you show.