Learn English – the word to describe the placement of two contrasting ideas next to each other?

The word you want is pleonasm:

Pleonasm (/ˈpliːənæzəm/; from Greek πλεονασμός (pleonasmós), from πλέον (pleon), meaning "more, too much") is the use of more words or parts of words than are necessary or sufficient for clear expression: examples are black darkness, burning fire. Such redundancy is, by traditional rhetorical criteria, a manifestation of tautology. That being said, people may use a pleonasm for emphasis or because the phrase has already become established in a certain form.

A context-relevant excerpt from the article body:

Redundancies sometimes take the form of foreign words whose meaning is repeated in the context:

• "We went to the El Restaurante restaurant."
• "The La Brea tar pits are fascinating."
• "Roast beef served with au jus sauce."
• "Please R.S.V.P."
• "The Schwarzwald Forest is deep and dark."
• "The Drakensberg Mountains are in South Africa."

At chux's request, here are some examples without foreign phrases, courtesy of Mental Floss:

• Nape of the neck
• Gnashing of teeth
• False pretense
• Safe haven
• Bleary-eyed
• Veer off course

If the term is too technical for you, you could simply say that saying Loch Ness lake is redundant.

(Source: Wikipedia)

I'd say the answer to your question depends on the manager's intention in using the phrase. If the manager is deliberately employing contradiction for rhetorical effect, then this is an oxymoron, as described here. If the contradiction is unintended, then it's merely a contradiction in terms or, if you want to be fancy (as Wikipedia does), a contradictio in terminis.

A good example of an oxymoron comes from the song "Mean Woman Blues," written by Claude Demetrius and recorded by Elvis Presley and others:

She kiss so hard, she bruise my lips

Hurts so good, my heart just flips.

Here, "hurts so good" is an oxymoron, because Demetrius is deliberately using the contradiction inherent in the phrase to produce a particular effect.

Similarly, Truman Capote's famous description of his book In Cold Blood as a "nonfiction novel" was also oxymoronic. Capote was of course well aware that novels are by definition works of fiction; he used the deliberately contradictory term "nonfiction novel" to draw attention to the literary qualities of a book that was (he claimed) a factually accurate work of reportage, and to highlight his contention that he had invented a new genre. As with Demetrius's "hurts so good," the contradiction actually sharpens the intended meaning, rather than obscuring it.

On the other hand, consider the following passage, from a book I'll refrain from naming:

A perfunctory perusal of literature in neuropsychology or the lucid writings of Oliver Sacks, if pressed for time, is all that we need to convince ourselves how sensory experiences can be unarguably real to one person whilst they are not even figments of another’s imagination.

Clearly, this author is not using the self-contradictory phrase "perfunctory perusal" for deliberate rhetorical effect, but is one of those benighted souls who think that "perusal" means the exact opposite of what it actually means. Thus, "perfunctory perusal" is not an oxymoron, but a mere contradiction in terms. The contradiction muddles the meaning, rather than enhancing it.

I should note that many native speakers regard "oxymoron" and "contradiction in terms" as synonyms and use them interchangeably. Personally, though, I find that the distinction between intentional and unintentional contradiction is worth trying to preserve.