I was on this flight as well and the captain can be quoted as saying "...one of the crew says that the floor doesn't feel good." My immediate thought was to ask if we could offer it some tylenol and a hug and get on our way. Like the OP said, it only took about 15 minutes after deplaning was completed for the announcement of "The aircraft is unserviceable" to be made.
Total delay was 1hr 45min which isn't so bad considering the effort to move passengers, crew, baggage and catering. The only thing that stood out to me in the whole process was the revised departure time on the display. Overly optimistic is probably the best way to describe it. For example, it said 8:40 when, at 8:10, the inbound replacement plane was still deplaning. It was obvious to me that there was no way we were making that time. I overheard many conversations where people were re-assuring their rides/family/etc that they would be leaving at 8:40 and arriving by 11:40 or actually making connections in Halifax. By no means am I suggesting that AC should have pushed to get us out by 8:40, but being more realistic with the departure time would have saved their customers from a number of cascading, non-AC controlled, scheduling failures.