For about 10 months now, match play wins against higher tiers have had an effect on average and thus on the tier. You might want to read the FAQ - match play section - to verify this.
The official justification for the implementation was
"Anti-Sandbagging", as wished by many players, but it's transparent that it would also force
players to buy equipment earlier to keep pace with the harder conditions.
Your match win dropped your average by 0.9 points and below the Master threshold of 67 => a tier-up - congratulations!
Nevertheless, you may continue as a TP in all tournaments that you started as a TP. Good luck for the Michelin!
Curiously: Was there credits at stake in the match?