I'm not really sure why its disappointing that they left some money on the table... maybe the statement is just incomplete. They could have easily offered the rest of their bonus pool to one of the players they did sign and then they wouldn't have any of that pool money left. Signing 18 of their top 20 picks (including the first 17) seems pretty decent.
It's not so much whether they did or did not offer the 200K to one of the HS kids drafted very low, it's that they drafted a bunch of college relievers early instead of getting another high upside HS kid in the top 10.
Out of 40 selections it looks like the Twins drafted and signed only 4 HS players? That seems like a pretty poor stratification from the talent pool, when they had the means to do better.