He was? That's news to me but you well may be right. I could have confused the details it's been a while. I remember there was a game in that match which was interrupted till the next day (they used to do it after I believe 40 moves) at the endgame stage and Bronstein made an elementary mistake the next day. Anything's possible but it's hard to believe that a player at this level would have made such mistake after having the whole day to analyze the position.
Just with pure Wikipedia-ing... Mikhail Moiseyevich Botvinnik was an assimilated Jew. Bronstein might have seemed "more Jewish" for all I know and so not have been considered desirable.
Also, terrible mistakes aren't unheard of in this level of play - I remember an account of the Karpov/Korchnoi match mentioning a few. The pressure in such a high level match is intense. Remember, no one has a day to analyze their next move. One player seals their move and it isn't revealed till the next day. True, they each get to think about the position in general but that's harder.
