Why did a migrated child link to an unrelated existing parent?

import {DatabaseSync} from 'node:sqlite';
import {TextDecoder} from 'node:util';
import {inflateSync} from 'node:zlib';
import {posix} from 'node:path';
import {createHash} from 'node:crypto';
const rows=(db,sql)=>db.prepare(sql).all().map(r=>({...r}));
const failed=(action)=>{try{action();return null;}catch(e){return {code:e.errcode??e.code??e.name};}};

import assert from 'node:assert/strict';
const run=function run(i,corrected=true){
    const db=new DatabaseSync(':memory:');try{db.exec('PRAGMA foreign_keys=ON;CREATE TABLE parent(id INTEGER PRIMARY KEY AUTOINCREMENT,label TEXT);CREATE TABLE child(parent_id INTEGER REFERENCES parent(id));');
      for(const id of i.existing)db.prepare('INSERT INTO parent VALUES(?,?)').run(id,'Existing');
      const newId=Number(db.prepare("INSERT INTO parent(label) VALUES('Imported')").run().lastInsertRowid);
      const mapping={source:i.sourceId,target:newId};
      const error=corrected&&i.childSource!==i.sourceId?'unmapped-source-parent':failed(()=>db.prepare('INSERT INTO child VALUES(?)').run(corrected?newId:i.childSource));
      return {mapping,error,parents:rows(db,'SELECT * FROM parent ORDER BY id'),children:rows(db,'SELECT * FROM child')};
    }finally{db.close();}
  };
const cases=[{"label":"misleading base","input":{"existing":[7,100],"sourceId":7,"childSource":7},"expected":{"mapping":{"source":7,"target":101},"error":null,"parents":[{"id":7,"label":"Existing"},{"id":100,"label":"Existing"},{"id":101,"label":"Imported"}],"children":[{"parent_id":7}]},"corrected":false},{"label":"corrected base","input":{"existing":[7,100],"sourceId":7,"childSource":7},"expected":{"mapping":{"source":7,"target":101},"error":null,"parents":[{"id":7,"label":"Existing"},{"id":100,"label":"Existing"},{"id":101,"label":"Imported"}],"children":[{"parent_id":101}]},"corrected":true},{"label":"coincidental source-target number equality","input":{"existing":[],"sourceId":1,"childSource":1},"expected":{"mapping":{"source":1,"target":1},"error":null,"parents":[{"id":1,"label":"Imported"}],"children":[{"parent_id":1}]},"corrected":true},{"label":"unmapped child source","input":{"existing":[7,100],"sourceId":7,"childSource":8},"expected":{"mapping":{"source":7,"target":101},"error":"unmapped-source-parent","parents":[{"id":7,"label":"Existing"},{"id":100,"label":"Existing"},{"id":101,"label":"Imported"}],"children":[]},"corrected":true}];
for(const test of cases){
  const actual=run(test.input,test.corrected);
  assert.deepEqual(actual,test.expected,test.label);
  console.log(test.label,actual);
}