Let's talk about our Red Rush strategy...

There's no need for that because, in that way, blue could specifically block the portal/underground gate, hindering red, for example, from bringing troops to the main hero.

And if red can see it, what changes in your logic?

Pete's suggestion is aimed at preventing accidental rush attacks, where one player is advancing and suddenly gets rush attacked.

In the CIS Championships, a similar interpretation to Pete's was used, only the increase from hidden units (previously painted) and portals (previously built) was still counted as an increase.