I had a run training this morning, after it, Race Predictions updated (presumably as VO2Max marginally increased).
In the evening, I had a swim training in the pool. After it, Race Predictions updated, significantly dropping the expected pace.
Checking with Runalyze seems to confirm the swim activity had Performance Condition and VO2Max values in it. Obviously I can't swim quite as fast as I can run. I have both activities if someone from Garmin wants to investigate.