Resigning In A Won Position

I PLAYED at Bradford over the weekend, hoping to repeat last year's feat of winning the U171 tournament.
Instead, I had one of my worst congresses ever, despite facing five players graded 117-147, ie considerably lower than my 169.
I had losing positions in every game, but somehow managed to scrape together a 50 percent score.
I was much helped in this by my round-three opponent resigning in a won position.
Here is the game after White's 50th move:

Spanton (169) - Dennis J Wright (141), Bradford U171, 2017

Seeing he was about to lose his pinned bishop, my opponent played 50...Rxe2, desperately hoping I would fall for 51.Kxe2 Qa6+, when Black picks up White's bishop and has an attack against the exposed White king.
But I was ready for this and so played 51.Qxe2, prompting DW to immediately resign.
It was only later that evening, putting the game into my database, that I realised - thanks to analysis engines - that Black, not White, is winning after the simple 51...Qxf5+.
True, White can save his bishop with 52.Bf2, but the engines have Black winning easily with 52...Bb6. Materially, Black has only a pawn for the exchange, but there is much more to come thanks to the exposed nature of White's king.
On a brighter note, the congress, held upstairs at Bradford Latvian club, featured good playing conditions and, an increasing rarity these days, a well-stocked bookstall.

Players gathering before round four on Sunday morning