Well, technically they can issue the I-94 for whatever time period they choose...However, they do tend to give them for 6 months but it is no guarantee. This individual that only got the 2 day I-94 is one of our V.I.P clients as he has 9 pages of criminal offences for certain things. He told me the border guard looked in the computer and looked his name up and suddenly got really stern with him because of what was in the system. The guard was trying to tempt him into a verbal fight so that he could get his waiver revoked. Luckily, he did not fall for it and the next day got a much nicer officer. So they do treat people differently depending on the person and the officer.
The point is that some of these officers can be cowboys(at least in BC) and we have to also take this into account when we give people their packets and send them to the border.
Another example is that the Sumas Border is the worse one in the lower mainland and there they have a habit of really grilling people and sometimes will try to find a reason to revoke a valid waiver. Apparently, it is a training border and the new guys try to make a good impression on management.