I'm just starting law school so take what I'm saying with a grain of salt, but this is a pretty interesting case since I'm studying offer and acceptance right now in contracts class. It's a bit difficult to analyze this since the facts are scarce. A good case to look at for reference is Butler Machine Tool v. Ex-Cell-O Corporation.

The variations Arganov proposed in his counter-offer were pretty extreme: he made significant changes to the material terms. He also didn't appear to do anything to bring Tinkov's attention to these variations and made the counter-offer look very similar to the initial offer (i.e: it looked almost identical). I don't see any mention that he highlighted the variations, or included a note bringing Tinkov's attention to them, or asked Tinkov to initial beside them. At this point, I would say that Tinkov didn't consent to the variation and had assumed that Arganov had accepted their original offer.

BUT, since they apparently gave him the unlimited line of credit he had included in his counter-offer, it seems pretty conclusive that by their conduct they had in fact accepted Arganov's counter-offer.

[https://en.wikipedia.org/wiki/Butler_Machine_Tool_Co_Ltd_v_E...]