Murphy isn’t a sore loser. He’s always been a gentleman in defeat and victory. His comment was very poorly timed, and he knows that. His statement about Si not facing the same pressure as professionals was purely about that first round match, not about the pressures of life as an amateur in a foreign land, etc. Si is doing his thing and suddenly gets a call up to play in the UK Open. His spot on the tour isn’t at risk, he’s not playing for ranking points, success in the event won’t change his amateur status, even if he wins the event. He quite literally has absolutely nothing to lose. A number of other pros/former pros agree with him primarily because there is a very well established and grueling process for gaining the right to play in professional events, and topping up events sidesteps that process.
Sean also wasn’t targeting Si. He congratulated him after the match, he apologized to him for his comments detracting from his win. He was being critical of the process.