Why if statement and && don't behave similarly in this case?

I have a function in a script that returns an exit code of 0 if a given line number exists in a file, otherwise it returns an exit code of 1. This is its current structure:

lineCont=$(sed "$1!d" "$dbFile")

if [ -z "$lineCont" ]; then
    return 1
fi

If I try to replace the if-statement with [ -z "$lineCont" ] && return 1 it will return an exit code of 1 even if the line actually exists in the file. Why this happens?