Grammar analysis: why is "Fufu" in the following sentence object complement rather than direct object

The explanation given in the Oxford Advanced Learner's Dictionary makes the distinction clear. In this dictionary the pattern "VNN" is that for transitive verbs with a direct object (N) and an indirect one (N), the objects being noun phrases. the patterns "VN-N" and "VN-ADJ" are those of transitive verbs that have a direct object and a complement (which can be a noun phrase (-N) or an adjective (-ADJ).

The way to tell between "VNN" and "VN-N" is that in this latter case the noun phrase "-N" tells something about "N", the object of the verb.

In "I give my pug some water.", "water" tells you nothing about the pug. In "I call my pug Fufu.", "Fufu" tells you that the pug has a name and what that name is.

Examples from OALD

• She considered herself lucky. VN-ADJ
• They elected him president. VN-N
• I sold Jim a car. VNN