This is just a superstitious believe by some gamblers because it's not totally true that when you have a negative feelings it will affect your luck, these luck in question happens randomly irrespective of how someone is feeling but being anxious is just like a natural feeling that some people have when they go gambling because they are scared off losing.
There are some individual that they get more lucky when they're anxious and not when they're feeling so confident. Luck works in different ways for different individual therefore nobody should tell you there's a particular way that it works. The only bad side to anxiety that I can think of is that it can make you to pick the wrong choice than what you're supposed to pick because you're doubting yourself but this can be a blessing in disguise too . If you wanted to pick a particular team because you believe that they're going to win and then anxiety make you to go with another choice, you can get lucky and your new team gets to win.
That's why I don't believe that luck works according to someone's feelings because if it doesn't many people will be winning when they are feeling confident about their bet. Like the example you game, it's possible that an anxious person can even pick the right game too in that state of mind but it might also be the other way round, luck can just be magical most times.