Yes, it's a coincidence.
The TGA promo without the update would have been basically a zero bump. This update without the TGA promo would have created almost the same bump. Update + TGA promo = what we got.
TGA promos don't generate huge CCU peaks. Many games already released on Steam also got a TGA promo and none of them got this bump. This one got it because it had a ton of content that a lot of players were asking for since months ago.
Big updates for GaaS with highly awaited meaty/important/heavily awaited content like this one (new enemy faction + new setting + new vehicles + new weapon types + more) generates big CCU peaks without TGA promo. Example: when in SF5 or SF6 -or fighting games in general- the game gets a new beloved character or gets a big rebalance update that fixes some issues the player were asking to fix.