Computer player - attacks/counterattacks. How it works ?

[Imp]

Not heard of quite as you describe but the AI can be unpredictable, normaly goes for the VHexes but have known it ignore them till half way through the game & make a B line for my rear area. It also is not uncommon for it to ignore them at the start heading straight past them & then swinging round, trying for a flanking move possibly.
In your case sounds like it did something along those lines & then decided to hold the routes to the Vhexes. It will probably decide to take them later in the game.
Sometimes these tactics make for a poor game but can also make for a very good one because its been unpredictable.