For me, there are three questions:
1) Should the try have stood?
2) Was the Ref correct to call time on?
3) Did Farrell screw up by calling the England squad into a huddle?
To the first question, Wales hadn't said that they were going for goal, the kicking tee wasn't on the pitch, time was called on, the ball was kicked from the mark, Josh Adams was onside and the grounding was good. Therefore there were no grounds to disallow the try.
With regards to calling time on, I think this happens more that we realise in this situation. Does the defensive line need to be set for kicks to the corner? I think the ref called time on expecting Wales to kick to the corner and was caught off guard, but as time was on, couldn't disallow the try. I expect a World Rugby directive to be released this week about when time on should be called to prevent this in future.
With regards to the third question, in my view, you should never switch off and go into a huddle when defending in your 22. I can't recall Dallaglio ever doing that. When a ref told him to speak to his players he would shout at them but leave them in the defensive line.
I do wonder how much of Farrell's reaction was down to how Eddie runs the England set up. I can't imagine him or Ford ever doing what Biggar did because Jones has them so regimented that they'd be dropped if they did regardless of the outcome (think Cipriani and May's try in the third test v South Africa in 2018).
In all honesty I've never understood why more sides don't do what Wales did if they have a chance. Had Jacob done the same thing and set up a match winning try on Saturday for Josh, I'd have been thrilled. Nothing wrong with being sneaky.