The Disney Reservation system has lots of wonkiness regarding party size. When I travel solo, there are many times that I don't get any results (or I'll get 1 90 minutes after my preferred, entered time). If I switch that from 1 to 2, suddenly a world of slots opens up. It's pretty well known by the CMs and has repeatedly been suggested by them to book for 2 (in this case).
The same issue presents itself with parties of 2 (to a lesser extent) as well as parties of 3 (to an extent between 1 and 2).
It has something to do with how the tables are actually loaded into the system, that sometimes it won't recognize space for a smaller party than a 4-top and it basically says "No, this is for 4, we can't sit 1 or 2 or 3 there, since this is for 4 people". (At least, based on my knowledge of database applications in general and knowing that this issue has persisted for several years, is my best guess and speculation).
Note that even though Le Cellier does have a cc-guarantee, that fee is only assessed if you either cancel on the same day of the reservation or you simply don't show up at all. Parties smaller than the booked number should not be charged any fee at all.