no one calls their language hindko in my family we call it punjabi mostly because its all part of punjab, just like potohari dont sy they are speaking potohari they would rather say they are speaking punjabi, same with sariaki people. reason being they are known as punjabi. but if you think its a dialect of punjabi then lets meet somewhere and have some conversation
by the way there are so many common sindhi words in Hindko that growing up in Karachi we had to take sindhi courses and I would ace it while other fail or barely pass it
examples,
if you have to say sit here
punjabi will say "bay ja"
hindko will say "Ajh po or ajho cha"
sindhi would say "Ajho baba"
so is hinkdo a dialect of Sindhi or Punjabi