Why specifically mention Walsh?
It sounds like the target was the board but he didn't have the balls to directly attack them so went for Walsh instead.
Because Walsh is the DoF he's the transfer man.
Koeman gives his requirements, Walsh finds the players, tells Koeman who's available, then starts negotiations, advises the board of what they'd cost and what not to pay and what is fair price.
Everton have always been slow as anything at getting deals done, unless it's transfer deadline day. If Schneiderlin fits Koeman's requirements and is available at £24m, Moshiri can provide the money, but Walsh is telling them that's too much and to go at £19m then of course Koeman is going to be pissed at him. And annoyed with the board that they're not getting the players he require to improve the squad.
Lookman to me seems like a Walsh signing, Schneiderlin is a Koeman signing, he's worked with him before he knows what he'll bring to the team.