I'm honestly interested in watching the gallery/BTS for this. I want to know if they did the BoBF teaser as a bit of fun before they had any other writing in place. Were they like "oh crap, now what do we do", or was it all planned out.
Based off the recent interviews with Tem and Ming-Na, and some other BTS footage from other productions, it seems that Tem and others were cognizant of how Fett stands/walks/holds his blaster/ doesn't say much, etc. I seriously doubt they just forgot all that, so that brings me to writing and direction. The Fett we see in mando s2 seems to be decidedly more alike to what we expect, so it would seem that there were clear directions for the character to change drastically for this show.
I'm not saying they set out to destroy anyone's childhood, but I think there may have been a serious miscalculation as to what they thought people wanted to see from this. It wouldn't surprise me if we see some big twist soon, as this all feels so out of place for the characters/world/ story, but hopefully they take notes and don't experiment with the recipe like this again.