CK,
There are several reasons why these engines can emit smoke at startup. One must first determine if the smoke is blue, white, or black in order to begin the diagnosis process.
Your mechanic offered some sound advice IF he gave the context for his statement.
Fact is, very very few people truly understand these dry-sump oiling systems and tend to maintain their oil levels (hot) at or near the top mark on the dipstick. In some cases, people unknowingly overfill the system by not allowing the oil temp to get up to operating temperature before making a decision about oil level. Adding oil when the temps are below 185 deg F is a sure cause for excess smoking.
964's are really good cars and I would recommend availing yourself about these engines and reading up on them (the owner's manual is a great place to begin) so you understand the systems and differences.
One quart is inconsequential in a system that holds 14 quarts.