While that may end up happening, Curran's report that the Tweet/graphic is based on was him speculating after the Germany game. He made it very clear during his original info on this that he thought that was what was happening, not that he was told it is happening.
It all boils down to how his patience and strike zone knowledge translates when pitchers are throwing more strikes than he's ever seen, and better quality strikes at that. Does the strikeout rate spike and power dip because he's still trying to wait out pitchers, or did he adjust and swing more at pitches he can drive?
The problem is his stuff had been that volatile since he was on the prospect radar. You could see home one start in HS and he'd be electric and the next he was completely ordinary.
Barring a completely catastrophic turn of events (think major medical flags or the kid just straight walking away), this deal gets done. They knew exactly what he wanted before they picked him and don't make the selection that high without it being a 99% certainty. Once they drafted McGonigle, their math and draft decisions included his number.
High round picks there is very little doubt what the number/terms are. Lower round picks there can be some uncertainty, but they always have a good idea even on the low round guys. That's where your area scouts make their money....building the relationship with the player/family, and knowing what it will take to sign them.