Nominals (nouns and pronouns), adjectives, prepositions, subordinators (subordinate conjunctions), and some adverbs can be predicative expressions: https://en.wikipedia.org/wiki/Predicative_expression. The notion that a predicative expression must be an adjective or noun is too narrow. While it is true that adjectives and nominals are widely acknowledged as functioning as predicative expressions, prepositions, subordinators, and some adverbs can clearly also be viewed as predicative expressions at times.
Thus in the example in the question, the preposition under is a predicative preposition, and the participle/adjective misleading is also a predicative expression. Here are some more examples:
a. It is on the table.
b. The game was after school got out.
c. That is soon.
The preposition on, the subordinator after and the adverb soon are predicative expressions. Note that participles (present active and past passive) are predicative expressions too (in fact, they are the canonical type of predicatives), e.g.
d. It is happening.
e. It is done.
The present progressive participle happening and the past passive participle done are predicative expressions.
The following article provides a good overview of what predicates and predicative expressions can be interpreted as being: https://en.wikipedia.org/wiki/Predicate_%28grammar%29. I think real insight about the nature of predicates comes with knowledge of predicate-argument structures. Modern theories of syntax and grammar draw a three-way distinction; they acknowledge predicates, the arguments of predicates, and the adjuncts on predicates. Consider the following example in this regard:
f. The book is on the table.
If one views the two-word combination is on as the predicate, then this predicate takes the two arguments the book and the table. This approach to predicates requires, however, that one jettison the (in my view erroneous) stance that the predicate in such a sentence is the entire string is on the table. The traditional binary division of the clause into a subject NP and a predicate VP is not supported by emperical considerations.
I will conclude this answer with a mysterious aspect of predicative expressions. Some adverbs can be predicative expressions, such as soon in the example above. Other adverbs, however, cannot function as predicative expressions, in particular those ending in -ly, e.g.
g. *It is happily.
h. *That is necessarily.
Why adverbs ending in -ly cannot function as predicative expressions, but most all other word categories can, is mysterious to me.