I won the round and both forfeited on the last putt of the round. What is the reason for doing that? Is it a way to not have the round count?
Yes, players "protect" their averages.
And by the way the Tour Champion is not great player. Is this how he rose up levels? Basically forfeit at the very end if it is not a great round?
A quitted round doesn't count to anything (except for a few XPs). Win or loss of a MP stroke play round won't be recorded anywhere outside the round itself.
In no way will such forfeit bring anyone closer towards their goals.
1) The ranked round count remains unchanged. That way, no step towards saturation.
2) There are less XPs, since the "completed" boni go missing => lower level, lesser clubs.
3) On the long run, "bad" rounds do not affect the average. This is due to the non-linear accounting once saturation has been achieved: Bad rounds will be kicked out early, leading to a noticable drop of the average.
Another point goes into quitting early and restarting (solo rounds): You fail to learn the back holes - it will take you longer to excel!