I think the explanation lies on a more local scale.
There's mention in the article about a seabreeze front which sweeps inland when the river was still.
Imagine if there was an easterly that day.
As the land warmed up, that would be directed upwards and 'suck' the cooler air in from the sea.
Where the two meet would be the front.
If the front is inland to you, you'll say 'seabreeze'.
What's happened, is that front was
just inland that day and then it shifted further out to sea. (It isn't a straight line up-down the coast either, hence better seabreezes on different parts of the coast)
Check out yesterday's graphs for Perth! That front sat in between Rotto and Swannie / Ocean Reef between about 4-7pm (but was non-existent OR west of Rotto at other times). The easterlies blew that rising hot air out to sea before it could go upwards properly.