Thanking God is not a form of proselytizing, unless that's the purpose of it. And you don't know their intent. I know for all my kids who participated in sports, and myself, that when I thanked God it was purely to make sure my Creator wasn't snubbed, but honored by me, and not forgotten. For a Christian, not giving glory to God in a moment on the big stage has a bad historical connotation.
Acts 12:21–23 - 21And on an appointed day Herod, having put on his royal apparel, took his seat on the rostrum and began delivering an address to them. 22And the people kept crying out, “The voice of a god and not of a man!” 23And immediately an angel of the Lord struck him because he did not give God the glory, and he was eaten by worms and died. (NASB)
Herod had killed James the apostle and tried to kill Peter, but that didn't bring God's wrath. But these circumstances of not giving glory to God did. I doubt there's a Christian on earth that thinks if they don't give glory to God on a stage they will die, lol, but it does prioritize things for the Christian.
And notice I just quoted a Bible verse with zero idea of proselytizing.
Of course, I respect your right to cringe.