In short
BoM and Seabreeze serve different products — differences are normal.
They can be — and that is often expected.
The Bureau publishes official public forecasts. Seabreeze emphasises wind and coastal conditions for watersports, using model guidance and presentation choices aimed at that audience. Different products, different emphasis; neither is “the only truth” for every beach hour.
More context: why forecasts feel wrong, vs other sites.