If memory serves correct, Dellavedova had signed the offer sheet and it was announced that the Cavs would not match prior to the Cavs working out the deal to acquire Dunleavy. It was originally announced that Dunleavy would be absorbed into a pre-existing TPE, which I believe was created when Varejao was traded. Essentially, the two moves were separate.
The Dellevedova contract started with a similar cap figure to Dunleavy's deal. The Cavs opted to structure Delly's departure as a sign and trade to create another TPE. This TPE wasn't quite large enough to absorb Dunleavy's deal, so the Cavs got Milwaukee to increase Dellevedova's starting salary by a few hundred thousand (and sent Milwaukee the extra money to cover it). In effect, this created a TPE from the Dellevedova departure that was just barely large enough to absorb Dunleavy's contract.
The benefit of all that maneuvering was that the larger TPE from the Varejao trade remained intact at it's full value, which is valuable since it can't be combined with other trade assets for salary cap matching purposes.
In theory, the Cavs could have matched Delly's deal and acquired Dunleavy with their existing TPE as this would have worked under the league's salary cap rules (but not necessarily within the Cavs budget restrictions due to the extreme luxury tax payments they'd be on the hook for).
