From what I understand this only applies for a tourist visa and although they indicate that the visa is similar to the Schengen visa in Europe there are distinct differences.
For instance, if a visitor applies for a visa at a Thai embassy, the documents will be forwarded to its Cambodian counterpart for approval, which will have the authority to reject the application, and vice versa. Also, visa fees for both countries will have to be paid. For instance, the Thai embassy will charge Bt1,000 for entry into Thailand and the tourist will have to pay the Cambodian visa fee upon arrival in that country and vice versa.
As per details provided by the Thai Foreign Ministry, neither country will issue a "multiple-entry" visa.
Source: http://nationmultimedia.com/national/Single-entry-visa-for-Thailand-Cambodia-30196863.html