bear trap memory

What does "bear trap memory" mean? Or bear-trap memory? Any why "bear trap"? I googled and saw a few examples. But none is very explanatory. An example of usage:

... I was caught by his bear trap memory of grammar again. ...

A bear trap is a trapping device for large animals. Once it has something trapped, it doesn't let go.

Someone has a bear trap memory if, having learnt something, they never forget it.

I'm much more familiar with a similar phrase:

She has a mind like a steel trap.

Which means that, in addition to having a strong memory (that grabs onto facts and never lets them go), also suggests that a person quickly understands and assimilates new concepts. See here and here:

have a mind like a steel trap: to be able to think very quickly, clearly and intelligently

from the Cambridge Idioms Dictionary, 2nd ed.

I think what the speaker means is that the person they are referring to has an excellent memory for grammar and never forgets. The speaker made a mistake in their grammar and the other person noticed it.

A bear trap is a mechanical device that is powerful enough for a bear to trap and hold a bear. Considering that bears are very large and strong animals, this phrase is supposed to show how good the person's memory is: once it holds something, it never lets go!

I don't know how common this phrase is. I don't hear it very often.