Them being on the ice had nothing to do with the goal.
I mentioned them more so as an easy way to point out Hakstol's personnel decisions in a close game. When the games get tight he goes to his reliable players and sometimes those reliable players aren't the best player and sometimes bad things happen when your best players aren't on the ice.
I'm not one to spend a lot of time playing the blame game after goals. Hockey is fluky. Guys make egregious mistakes that don't get talked about as long as the puck doesn't end up in the back of the net. Less egregious mistakes get talked about for pages when the puck goes in the net and certain players are on the ice. On any given goal against you can probably blame 3 different guys and not be wrong. So if you say MacDonald and Hagg "had nothing to do with the goal" you're just looking at the 3 second sequence before the goal and not the bigger picture.
How did the puck get in our zone to begin with?
MacDonald practically lets Nosek walk into the zone with controlled possession even with Simmonds providing back pressure towards the boards. Nosek is not exactly roaring through the neutral zone with speed and we are talking about a bottom 6 guy to begin with (Simmonds is gliding, that's how slow Nosek was moving). It's not a good play. Soon after Hagg and Couturier chase a loose puck, get their wires crossed, both defensemen end up on the same side of the ice, Eakin is wide open to receive a seam pass and the rest is history.
While it's not a mistake in the traditional sense by MacDonald, it's a lack of aggression that leads to zone time for the other team and ultimately a goal. This is part of the reason people point out these decisions even when the end result is a win. Long-term, these players that have a tendency to "generate defense" they end up hurting you. No matter how safe and reliable you may appear to the coach, if you play in your own zone long enough, the other team is going to outscore you.