There are two ways we can look at this issue then, L.S.
Using your argument along the lines of offer-acceptance, it is the employer who has accepted the offer NOT the employee.
Kajai made the employer a counter-offer. A counter offer is a rejection with a new offer. The rejection was the contract that included a 'restrictive covenant' clause, the offer was for the prospective employee to offer his services to his prospective employer under the original terms and conditions EXCEPT the restrictive covenant. The employer clearly accepted this!! The problem for Kajai (as stated earlier) is perhaps a lack of proving this acceptance of his counter-offer.
But even then, the restrictive covenant clause is voidable. I've read up on it tonight and it seems to be that it's validity very much depends upon the nature of the indvidual employer/employee relationship and how close the employee gets to any trade secrets or other confidential information of the company. A restrictive covenant will not be upheld simply to prevent a competitor hiring the services of a rival companies employees. However the fact that Kajai was a 'consultant' does not auger well.