I think the studio wanted the audience to believe it was either our Pietro resurrected with a different appearance or the Fox Pietro.
Okay but
why would the studio want the audience to believe that? It's only something the audience, not the characters, would be attached to and ultimately that is what ended up happening with the portion of the audience and that same portion ended up very disappointed.
And again, there is no way the studio wanted the audience to believe this was MCU Pietro. By casting the other actor portraying the character coupled with the audio file, it was obvious they were only going for the contrary.
For story reasons, they didn't want to use Aaron Taylor Johnson because they wanted to emphasize dead is dead and he can't be brought back, but they also didn't want to use a completely new actor since the audience would immediately go to the theory that it was a random stranger who wasn't Pietro.
The director explained the story reasons not to use Aaron Taylor Johnson and I already explained why I see a fallacy in his explanation. He said they could have brought back ATJ, but didn't, because the show already had a loved one brought back to life in the form of Vision. But bringing Vision back was all Wanda's own doing, we literally saw her bring him back. She was aware that it was her own power as the causation for that action. But if MCU Pietro was at her doorstep at the end of episode 5, she would have been astonished to the tenth degree because it was
not her own doing, and it comes right off of the heels of the heated conversation she and Vision were having on the couch in the preceding scene.
Again...to Wanda, the Fox Pietro in the X-Men universe might as well be a stranger. If it was eventually revealed to her that this stranger really was a person with the same identity as her brother from alternate universe, she would remain emotionally unchanged because that person is
still not her brother. She would not care. The only party that would/did care was the audience. The studio was banking on this fact, they were counting on it and what ended up happening was that that portion of the audience was left disappointed. If that isn't the studio trolling the audience, then I don't know what it is.